core.sharedRepository. Prompted by #867603.
* dgit-badcommit-fixup: Honour core.sharedRepository.
Closes:#867603.
+ * dgit: clone multisuite works even without --no-rm-on-error.
+ Closes:#867434.
* infrastructure: Cope with new git-receive-pack which has
quarantine feature: ie, work around #867702.
* test suite: Cope with git restricting ext:: protocols.