While looking at a different codebase, I was made (re)aware that the
ordering for APR to find the temp directory uses the following ordering
in env-vars:

           $TMP
           $TEMP
           $TMPDIR

with the rationale that "this is how Python 2.2 does it"

But really, the canonical var to use is $TMPDIR, and looking
over Python 2.6 (at least) does revise the ordering to be what
"should" be expected....

     for envname in 'TMPDIR', 'TEMP', 'TMP':
         dirname = _os.getenv(envname)
         if dirname: dirlist.append(dirname)


Anyone have heartburn if I "fix" tempdir.c ?