LU-1030 build: allow diff/chmod/deleted in commit-msg

When we write a commit body, sometimes there may be a line with
diff right at the beginning.  This shouldn't cause the rest of
the commit message to be skipped.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Change-Id: I012345678901234567890123456789012345500c