Move outstanding changes commands from 'o' to 'T'

The main reason for this is that then these commands can have
the same bindings in VC-Dir buffers that they have under
vc-prefix-map.  'T' is a good mnemonic for "Topic" and a
serviceable mnemonic for "outsTanding".

* lisp/vc/vc-hooks.el (vc-prefix-map): Move 'o' to 'T'.
* lisp/vc/vc-dir.el (vc-dir-mode-map): New 'T' bindings.

doc/emacs/maintaining.texi

@@ -1712,6 +1712,9 @@ Do an incremental regular expression search on the fileset
 Apart from acting on multiple files, these commands behave much like
 their single-buffer counterparts (@pxref{Search}).
 
+@c Outstanding changes commands under 'T' are not mentioned because
+@c these are an advanced feature documented only in vc1-xtra.texi.
+
   The VC Directory buffer additionally defines some branch-related
 commands starting with the prefix @kbd{b}:
 

doc/emacs/vc1-xtra.texi

@@ -298,11 +298,11 @@ yet merged into the target branch.
 @cindex outstanding changes
 
 @table @kbd
-@item C-x v o =
+@item C-x v T =
 Display diffs of changes to the VC fileset since the merge base of this
 branch and its upstream counterpart (@code{vc-diff-outgoing-base}).
 
-@item C-x v o D
+@item C-x v T D
 Display all changes since the merge base of this branch and its upstream
 counterpart (@code{vc-root-diff-outgoing-base}).
 @end table
@@ -321,17 +321,17 @@ unpushed commits and uncommitted changes in your working tree.  In many
 cases the reason these changes are not pushed yet is that they are not
 finished: the changes committed so far don't make sense in isolation.
 
-@kindex C-x v o =
+@kindex C-x v T =
 @findex vc-diff-outgoing-base
-@kindex C-x v o D
+@kindex C-x v T D
 @findex vc-root-diff-outgoing-base
-Type @kbd{C-x v o D} (@code{vc-root-diff-outgoing-base}) to display a
+Type @kbd{C-x v T D} (@code{vc-root-diff-outgoing-base}) to display a
 summary of all these changes, committed and uncommitted.  This summary
 is in the form of a diff of what committing and pushing (@pxref{Pulling
 / Pushing}) all these changes would do to the upstream repository.  You
-can use @kbd{C-x v o =} (@code{vc-diff-outgoing-base}) instead to limit
+can use @kbd{C-x v T =} (@code{vc-diff-outgoing-base}) instead to limit
 the display of changes to the current VC fileset.  (The difference
-between @w{@kbd{C-x v o D}} and @w{@kbd{C-x v o =}} is like the
+between @w{@kbd{C-x v T D}} and @w{@kbd{C-x v T =}} is like the
 difference between @kbd{C-x v D} and @kbd{C-x v =} (@pxref{Old
 Revisions}).)@footnote{Another point of comparison is that these
 commands are like @w{@kbd{C-x v O =}} (@code{vc-fileset-diff-outgoing})
@@ -359,12 +359,12 @@ upstream repository's development trunk.  That means committed changes
 on the topic branch that haven't yet been merged into the trunk, plus
 uncommitted changes.
 
-When the current branch is a topic branch and you type @kbd{C-x v o D},
+When the current branch is a topic branch and you type @kbd{C-x v T D},
 Emacs displays a summary of all the changes that are outstanding against
 the trunk to which the current branch will be merged.  This summary is
 in the form of a diff of what committing and pushing all the changes,
 @emph{and} subsequently merging the topic branch, would do to the trunk.
-As above, you can use @kbd{C-x v o =} instead to limit the display of
+As above, you can use @kbd{C-x v T =} instead to limit the display of
 changes to the current VC fileset.
 
 This functionality relies on Emacs correctly detecting whether the
@@ -379,7 +379,7 @@ The variables @code{vc-trunk-branch-regexps} and
 @code{vc-topic-branch-regexps} contain lists of regular expressions
 matching the names of branches that should always be considered trunk
 and topic branches, respectively.  You can also specify prefix arguments
-to @kbd{C-x v o D} and @kbd{C-x v o =}.  Here is a summary of how to use
+to @kbd{C-x v T D} and @kbd{C-x v T =}.  Here is a summary of how to use
 these controls:
 
 @enumerate
@@ -425,7 +425,7 @@ described.  E.g., if the value of @code{vc-trunk-branch-regexps} is
 branch.
 
 @item
-Supply a double prefix argument, i.e. @w{@kbd{C-u C-u C-x v o @dots{}}},
+Supply a double prefix argument, i.e. @w{@kbd{C-u C-u C-x v T @dots{}}},
 and Emacs will treat the current branch as a trunk, no matter what.
 This is useful when you simply want to obtain a diff of all outgoing
 changes (@pxref{VC Change Log}) plus uncommitted changes.
@@ -433,7 +433,7 @@ changes (@pxref{VC Change Log}) plus uncommitted changes.
 @item
 @cindex outgoing base, version control
 Finally, you can take full manual control by supplying a single prefix
-argument, i.e. @w{@kbd{C-u C-x v o @dots{}}}.  Emacs will prompt you for
+argument, i.e. @w{@kbd{C-u C-x v T @dots{}}}.  Emacs will prompt you for
 the @dfn{outgoing base}, which is the upstream location for which the
 changes are destined once they are no longer outstanding.
 

etc/NEWS

@@ -2746,11 +2746,12 @@ current VC fileset.
 
 +++
 *** New commands to report diffs of outstanding changes.
-'C-x v o =' ('vc-diff-outgoing-base') and 'C-x v o D'
+'C-x v T =' ('vc-diff-outgoing-base') and 'C-x v T D'
 ('vc-root-diff-outgoing-base') report diffs of changes since the merge
 base with the remote branch, including uncommitted changes.
 They are useful to view all outstanding (unmerged, unpushed) changes on
 the current branch.
+They are also available as 'T =' and 'T D' in VC-Dir buffers.
 
 +++
 *** New user option 'vc-use-incoming-outgoing-prefixes'.

lisp/vc/vc-dir.el

@@ -397,6 +397,8 @@ That is, refreshing the VC-Dir buffer also hides `up-to-date' and
     (define-key map (kbd "M-s a M-C-s") #'vc-dir-isearch-regexp)
     (define-key map "G" #'vc-dir-ignore)
     (define-key map "@" #'vc-revert)
+    (define-key map "T=" #'vc-diff-outgoing-base)
+    (define-key map "TD" #'vc-root-diff-outgoing-base)
 
     (let ((branch-map (make-sparse-keymap)))
       (define-key map "b" branch-map)

lisp/vc/vc-hooks.el

@@ -1018,8 +1018,8 @@ In the latter case, VC mode is deactivated for this buffer."
   "O"   #'vc-root-log-outgoing
   "M L" #'vc-log-mergebase
   "M D" #'vc-diff-mergebase
-  "o =" #'vc-diff-outgoing-base
-  "o D" #'vc-root-diff-outgoing-base
+  "T =" #'vc-diff-outgoing-base
+  "T D" #'vc-root-diff-outgoing-base
   "m"   #'vc-merge
   "r"   #'vc-retrieve-tag
   "s"   #'vc-create-tag