[PATCH] Fix ICE with invalid OPEN ACCESS= argument

[François-Xavier Coudert]

> As the testcase below shows, gfc_resolve_open wasn't checking ACCESS=
> argument and thus not issuing needed diagnostics and later on dying on
> ICE in set_string.  Tested on x86_64-linux.

OK to commit on all branches you think of. Where did that bug-report
come from? Is that in bugzilla somewhere? I'm amazed we didn't see it
before today...

FX