P_tmpdir in g_get_tmp_dir ()

[Josh MacDonald <jmacd CS Berkeley EDU>]

I just encountered a problem because of the definition of P_tmpdir
on FreeBSD.  It is set to "/var/tmp", but that's not the best place
for random temp stuff to go, I want "/tmp".  There's a comment in
/usr/include/stdio.h saying:

/* System V/ANSI C; this is the wrong way to do this, do *not* use these. */
#ifndef _ANSI_SOURCE
#define P_tmpdir        "/var/tmp/"
#endif

so I thought perhaps it shouldn't be used.

-josh