ARS improvements:

Added HOST and IP keywords to allow restricted access/privileges to/for
specific remote hostnames or IP addresses (wildcards allowed).
All string-argument type ARS keywords (e.g. SHELL, PROT, etc.) now support .can
style wildcards.
The current remote client is now used for protocol, host, and IP ARS checking,
when available, so this requires passing the client pointer around (which
explains why so many files are touched by this change) and takes care of a
long standing to-do item (the user's 'modem' value was used for the PROT
value checking, which was not always correct).