Make sure P4Ruby picks up P4CHARSET from the environment.
Previously, our cached copy of the charset was not being
initialised, and that's why it wasn't being picked up. Rather
than initialise it, I've chosen to simply eliminate the cached
copy, and use ClientApi to store it. Simpler, and more reliable.
User-visible bug fix documented in p4rubynotes.txt
Note, as the job contains another request, it stays open for now.