bug#14169: vc: [bzr] Small nuissance when invoking 'log-view-diff-changeset'

[Lluís Vilanova]

When issuing 'vc-print-log', the results of "bzr log" have a line of '-'
characters prepended to every revision.

The net result is that point is set to the first line of the output, which is a
line with '-' characters, and 'log-view-diff-changeset' is unable to show the
diff for that line.

It also feels inconsistent that hitting 'D' on any other line of '-' characters
shows the diff for the previous revision (while that line is, in fact, a prefix
for the revision that comes below).

Thanks,
  Lluis