Garbage collection update.
Removed stale debug statement and
added what I think is correct support for garbage collection. Now
any Ruby vars supplied as input to a "p4 xxx -i" command will not
be swept while we're using them.
gc_mark() - Ruby's API function for the mark and sweep garbage
collector has a duff prototype in Ruby 1.6.4 and 1.6.5 so I've
had to add that here to keep GCC statisfied. Hopefully it can
be removed later on.