git push exits with zero status when hg rejects push with error:abort

[riastradh]

Version: git-cinnabar at commit 9827742

Configure an hg repository with the reject_new_heads hook, and try to push a new head:

$ git push origin
remote: adding changesets
remote: adding manifests
remote: adding file changes
remote: error: pretxnclose.reject_new_heads hook failed: Changes on branch 'default' resulted in multiple heads
remote: transaction abort!
remote: rollback completed
ERROR Changes on branch 'default' resulted in multiple heads
To hg::...
 * [new branch]      branches/default/tip -> branches/default/tip
$ echo $?
0

And origin/branches/default/tip is updated as if the push had succeeded, even though hg log on the upstream repository shows it has not.

Expected result:

1. nonzero exit status indicating that the push failed
2. origin/branches/default/tip is not updated

Full reproducer pushreject.t attached.