Add an option commitDiffOpts to customize logs for revisions

Added in the same way as logOpts/diffOpts.  The default is set to
"-C --stat -p --cc", which matches the previous behavior.

This option can be used, for example, to ignore whitespace when
creating diffs.

Signed-off-by: Eric Berberich <eric.berberich@gmail.com>
Merge branch 'commitlogopts'

Add an option commitDiffOpts to customize logs for revisions.