[PATCH] simpler test for PURGE method

This patch uses a tri-state setting on enable_purge and acl parsing to
detect PURGE method addition/removal instead of a complicated ACL
creation test post-configure.

This removes the annoying false errors about temp ACL and some minor
speed up in all actions that parse squid.conf.

Amos

-- 
Please be using
   Current Stable Squid 2.7.STABLE6 or 3.0.STABLE14
   Current Beta Squid 3.1.0.7