Merge branch 'jk/fsck-exit-code-fix'

"git fsck" failed to report that it found corrupt objects via its
exit status in some cases.

* jk/fsck-exit-code-fix:
fsck: return non-zero status on missing ref tips
fsck: exit with non-zero status upon error from fsck_obj()

diff --cc builtin/fsck.c
Simple merge