CARP peer selection cleanups

This work aims at cleaning up and finishing the CARP peer selection algorithm in Squid.

Issues to address

• --enable-carp is very aggressive and changes the meaning of cache_peer
• Only the CARP hashing algorithm is implemented. Need to fetch CARP membership tables
• The load factor needs to be normalized. It should be a load factor, not a percentage.
• Only a "CARP-client" is implemented, not inter-array CARP routing.
• CARP membership array manager is missing
• CARP peers needs to be sorted when calculating the hashes. It is not reasonable to expect the user to sort the peers properly.

Progress

• 2001-04-22: carp_load_factor replaced by normalized weight
• 2001-04-22: can now co-exists with other selection methods. CARP peers are marked by the new "carp" cache_peer option.