First, again my apologies for completely missing that you had posted this review!
I've finally found some time to take a look to the patch.
It applies with some fuzziness on master, but the result looks correct. Unfortunately the OID of the new pg_stop_backup function conflicts with "pg_blocking_pids()" patch (52f5d578d6c29bf254e93c69043b817d4047ca67).
Eh. There is no presence of "tblspc_mapfbuf" after the patch. I think it looks like the "applies with fuzziness" actually wasn't correct, and you ended up with bad code with a mix of the old and the new code in it.
I've attached an updated patch, which is rebased on current master and includes the oid fix.