Include X-Gerrit-ChangeId, X-Gerrit-Commit headers in emails

This may help automation tools to know the change id and the git
commit associated with the message, without needing to run off to
the Gerrit server's JSON interface, or rip apart the X-Change-URL
header to obtain the id component from it.

Signed-off-by: Shawn O. Pearce <sop@google.com>
1 file changed