[PATCH] adaptation_meta option

This option allows Squid administrator to add custom ICAP request
headers or eCAP options to Squid ICAP requests or eCAP transactions.
Use it to pass custom authentication tokens and other transaction-state
related meta information to an ICAP/eCAP service.

The addition of a meta header is ACL-driven:
         adaptation_meta name value [!]aclname ...

Processing for a given header name stops after the first ACL list match.
Thus, it is impossible to add two headers with the same name. If no ACL
lists match for a given header name, no such header is added. For example:

         # do not debug transactions except for those that need debugging
         adaptation_meta X-Debug 1 needs_debugging

         # log all transactions except for those that must remain secret
         adaptation_meta X-Log 1 !keep_secret

         # mark transactions from users in the "G 1" group
         adaptation_meta X-Authenticated-Groups "G 1" authed_as_G1

The "value" parameter may be a regular squid.conf token or a "double
quoted string". Within the quoted string, use backslash (\) to escape
any character, which is currently only useful for escaping backslashes
and double quotes. For example,
     "this string has one backslash (\\) and two \"quotes\""

This is a Measurement Factory project