Allow updates of commits where only the parent changes

This is necessary to support updates caused by a rebase, where the
parent commit didn't update its tree but perhaps only updated its
commit message, or the rebase is around a cherry-pick followed by
a revert.

Bug: issue 359
Change-Id: I2c53a4a5b11c2c90967b3ba0ea2452668f3f4723
Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed