src/libpcp/src/pmns.c: correct logic in __pmHasPMNSFileChanged()
src/libpcp/src/pmns.c: correct logic in __pmHasPMNSFileChanged()

One of the predicates was rewritten incorrectly in the last change,
also rework the diagnostics so the result of __pmHasPMNSFileChanged()
is also reported under the control of DBG_TRACE_PMNS.

adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp