Tablespace permissions issue

Chris KL just raised an issue on IRC:

test=> create table test (a int4) tablespace pg_default;
ERROR:  permission denied for tablespace pg_default

This wasn't encountered in my original patch because
pg_tablespace_aclmask() had this test reasonably early on:

+   if(tbloid == DEFAULTTBLSPC)
+       return (mask);

I guess that might have been a bit presumptuous but a similar thing
happens if you don't specify a tablespace:
       tablespaceId = get_namespace_tablespace(namespaceId);       /* note no permission check on tablespace in this case */

What should the solution be?

Gavin