Support showing a single log entry from vc-annotate.

* vc.el (print-log): Add a new argument: START-REVISION.
(vc-print-log-internal): Add a new optional argument and
pass it to the backend.
(vc-print-log, vc-print-root-log): Adjust callers.
* vc-annotate.el (vc-annotate-show-log-revision-at-line): If a
buffer already displays the requested log entry, use it.
Otherwise display only the log entry in question.
* vc-svn.el (vc-svn-print-log):
* vc-mtn.el (log-view-file-re):
* vc-hg.el (vc-hg-state):
* vc-git.el (vc-git-print-log): Add support for new argument START-REVISION.
(vc-git-show-log-entry): Return t on success.
* vc-bzr.el (vc-bzr-print-log): Add support new argument START-REVISION.
(vc-bzr-show-log-entry): Return t on success.
* vc-rcs.el (vc-rcs-print-log):
* vc-sccs.el (vc-sccs-print-log):
* vc-cvs.el (vc-cvs-print-log): Add new argument, ignore it.

1 files changed, 4 insertions, 0 deletions

diff --git a/etc/NEWS b/etc/NEWS
index f351fe9e16e..f6bc8fb0f2e 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -267,6 +267,10 @@ it displays the old names for the files and it can show logs/diffs for
 the corresponding lines.  Currently only Git and Mercurial take
 advantage of this feature.
 
+*** The log command in vc-annotate can display a single log entry
+instead of redisplaying the full log.  The RCS, CVS and SCCS VC
+backends do not support this.
+
 *** When a file is not found, VC will not try to check it out of RCS anymore.
 
 *** Diff and log operations can be used from dired buffers.