src/libpcp_pmda/src/queues.c: rework diagnostics in pmdaEventNewClient()
src/libpcp_pmda/src/queues.c: rework diagnostics in pmdaEventNewClient()

1. always report a new client
2. diags should be emitted vi fprintf to stderr, not

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