Ensure tmpdir used in vpmprintf always gets a sane value
Ensure tmpdir used in vpmprintf always gets a sane value

Recent changes in temporary file handling (BSD porting)
regressed a corner case exercised by test 448, where no
/etc/pcp.conf exists.  This resulted in invalid tmpfile
paths being requested (in the fs root), and EPERM ended
up being the result.

Fix to ensure we always get a sane fallback for tmpdir.

andyvand/cygpcpfans,aeg-aeg/pcpfans,aeg-aeg/pcpfans,aeg-aeg/pcpfans,tjanez/pcp,adfernandes/pcp,aeg-aeg/pcpfans,wuliming/pcp,andyvand/cygpcpfans,mbaldessari/pcp,prasincs/pcp,andyvand/cygpcpfans,wuliming/pcp,tjanez/pcp,edwardt/pcp,tjanez/pcp,adfernandes/pcp,aeg-aeg/pcpfans,wuliming/pcp,aeg-aeg/pcpfans,prasincs/pcp,tjanez/pcp,andyvand/cygpcpfans,prasincs/pcp,wuliming/pcp,mbaldessari/pcp,edwardt/pcp,aeg-aeg/pcpfans,prasincs/pcp,wuliming/pcp,ryandoyle/pcp_original,wuliming/pcp,adfernandes/pcp,mbaldessari/pcp,edwardt/pcp,adfernandes/pcp,ryandoyle/pcp_original,ryandoyle/pcp_original,ryandoyle/pcp_original,tjanez/pcp,wuliming/pcp,andyvand/cygpcpfans,prasincs/pcp,edwardt/pcp,edwardt/pcp,mbaldessari/pcp,mbaldessari/pcp,andyvand/cygpcpfans,adfernandes/pcp,edwardt/pcp,tjanez/pcp,ryandoyle/pcp_original,mbaldessari/pcp,wuliming/pcp,tjanez/pcp,ryandoyle/pcp_original,prasincs/pcp,edwardt/pcp,andyvand/cygpcpfans,adfernandes/pcp,adfernandes/pcp,aeg-aeg/pcpfans,ryandoyle/pcp_original,andyvand/cygpcpfans,tjanez/pcp,ryandoyle/pcp_original,adfernandes/pcp,prasincs/pcp,edwardt/pcp,prasincs/pcp