Correct return value of OpenBSD::MkTemp in scalar context

From Francesco Toscan < f.toscan AT hotmail DOT it >

ok guenther@

merge/resolve conflicts
(some more to do after this one)

In a scalar context, mkstemp should return just the file handle

"sure" espie@

Change the Perl->C wrappers for mkdtemp and mkstemps to behave more like
the File::Temp routines and call croak() (the C version of 'die') instead
of returning an empty list. This lets pkg_add give

Change the Perl->C wrappers for mkdtemp and mkstemps to behave more like
the File::Temp routines and call croak() (the C version of 'die') instead
of returning an empty list. This lets pkg_add give good error messages
when your $PKG_TMPDIR is mounted read-only.

ok espie@

show more ...

extra .xs glue to use mkstemp and mkdtemp directly
written by guenther@ about a year ago.
discussed with him and millert@