Only remake pmns file if it does not exist.
Only remake pmns file if it does not exist.

Part of the perl PMDA support was unconditionally remaking pmns and
domain.h ... this was reordering the metrics for the simple PMDA and
causing QA tests 255 and 578 to fail ... more importantly if the
pmns file already exists then there is no point in using the perl
PMDA magic to recreate it.

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