fix security PR1101: unprivileged access to linux proc.* metrics on modern kernel
fix security PR1101: unprivileged access to linux proc.* metrics on modern kernel

Switching to setres[ug]id(ID,ID,-1) from the prior sete[ug]id(ID)
appears to make kernel 3.17.4 behave as prior ones did, so as to
reject access by unprivileged pcp clients to others' /proc/$pid/ data.
(The open(2) still succeeds, but the subsequent read(2) gets EACCES.)

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