* rr/rebase-autostash:
rebase: implement --[no-]autostash and rebase.autostash
rebase --merge: return control to caller, for housekeeping
rebase -i: return control to caller, for housekeeping
am: return control to caller, for housekeeping
rebase: prepare to do generic housekeeping
rebase -i: don't error out if $state_dir already exists
am: tighten a conditional that checks for $dotest