Fixed an environment insulation bug in init scripts.
More testing (and thinking) revealed that the only way to truly
provide a guarantee of insulation from user-set defaults in
~perforce/.bashrc (etc.) is to pass SDP_INSTANCE as a parameter to
the *_base scripts, so that the instance name is explicitly passed
into the su/exec call (when run as root).
This change also includes minor cleanup in init scripts and *_base