Fix the backup script to handle duplicate revision id records

This happen when the same commit has been uploaded to two different
projects.  In Android this is possible with the Linux kernel, as
we have two forks of the kernel source as two different projects
and some changes were uploaded to both.

Its a bug in Gerrit's data schema that the revision key includes
the project key, permitting this sort of duplication.

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