cleanup; tmpfile now lets tmpnam allocate space for it, also checks

cleanup; tmpfile now lets tmpnam allocate space for it, also checks
result of tmpnam() call.  tmpnam() allocates space, doesn't use a static buf;
rewrite tempnam() to do no error checking, just depend on mktemp(3).

SCCS-vsn: lib/libc/stdio/tempnam.c 4.6