Document %%OSREL%%, %%PERL_VER%%, %%PERL_VERSION%% and the corresponding
PLIST_SUB. Update for new MAN? semantics. Accomodate USE_X_LIB and
USE_X_PREFIX. Add small para giving hints for porters on how to stay
current with bsd.port.mk.

Egged-on by: Bill Fumerola <billf@chc-chimes.com> and

		Don Croyle <croyle@gelemna.ft-wayne.in.us>