Merge branch 'jk/ok-to-fail-gc-auto-in-rebase' into maint

"git rebase", unlike all other callers of "gc --auto", did not
ignore the exit code from "gc --auto".

* jk/ok-to-fail-gc-auto-in-rebase:
rebase: ignore failures from "gc --auto"

diff --cc git-rebase.sh
Simple merge