Added p4dstate.sh to SDP.
Changes from originating server (no functionality changes):
* Adjusted Copyright message to SDP standard, which references
the same basic content.
* Added comment clarifying that RCS values are verbatim from
the originating Helix Server, and read-only elsewhere.
* Comments and usage instructions needed.
* SDP-ifiy it; i.e. have it take an instance parameter, and
which point all other settings (path to p4d and p4 executables,
P4ROOT and other environment variables) are known.