Remove all compatibility code with versions of the API older
than 2006.2 from both P4Perl and P4Ruby. We're insisting that
people use a 2006.2 or later API for this first release, and will
support the current API, and the previous two releases going forward.
Also stripped out some reference Ruby code that was still lurking
in P4Perl (commented out, obviously).
Also ensured that both Makefile.PL and p4conf.rb insist on the
minimum API level, and warn the user if they're attempting to
build with an even newer release of the API.