Merge branch 'jc/stash-drop'

"git stash drop" is reimplemented as an internal call to reflog_delete() function, instead of invoking "git reflog delete" via run_command() API. * jc/stash-drop: stash: call reflog_delete() in reflog.c reflog: libify delete reflog function and helpers stash: add tests to ensure reflog --rewrite --updatref behavior