Add an "AccountingRule" feature to permit limiting bw usage by read+write

Patch from "chobe".  Closes ticket 961.
Avoid frequent strcmp() calls for AccountingRule

Generally, we don't like to parse the same thing over and over; it's
best IMO to do it once at the start of the code.
Changes file for ticket 961
Merge branch 'ticket961_squashed'
Respond with 'Command not supported' SOCKS5 reply message upon reception of unsupported request.
Rename socks5 error code setting function again

I'd prefer not to use the name "send" for any function that doesn't
really send things.
Merge branch 'bug12971_take2_squashed'