Resolve a libpcp_pmcd / pmcd symbol shadowing issue with nAgents.
Also correct the external-declaration of the global agent pointer
which is pmcd-local, not externally in the library. These issues
caused different values of nAgents to be seen at different times
in pmcd startup, causing it to exit early (on Windows) thinking
no agents had been configured even though it had successfully set
up both the pmcd and windows DSO PMDAs.
Resolve a libpcp_pmcd / pmcd symbol shadowing issue with nAgents.
Also correct the external-declaration of the global agent pointer
which is pmcd-local, not externally in the library. These issues
caused different values of nAgents to be seen at different times
in pmcd startup, causing it to exit early (on Windows) thinking
no agents had been configured even though it had successfully set
up both the pmcd and windows DSO PMDAs.