pmmgr: restore ability to invoke as non-pcp/non-root
pmmgr: restore ability to invoke as non-pcp/non-root

commit 27c0e02db32d6 broke pmmgr's ability to be run as any ordinary
user, by mandating that it be able to report its pid in $PCP_RUN_DIR.
This level of strictness is unprecedented and unnecessary, so we don't
do that any more.

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