[PATCH] Reusable ACLChecklist

Hi all,

The problem has been discussed here:
   http://www.squid-cache.org/mail-archive/squid-dev/201105/0116.html

This patch add the method ACLChecklist::reusableFastCheck which is
similar to the ACLChecklist::fastCheck method but it can be called many
times, and each time called a new independed access list check done.

Also I found some problems in ACLChecklist::fastCheck which the current
patch does not try to solve them, but we may take care of.

1) Documentation of ::fastCheck does not match implementation
--------------------------------------------------------------
Currently the documentation of the ACLChecklist::fastCheck does not
match the implementation. From the documentation:

   * If there is no access list to check the default is to return DENIED.
  ...
   * \retval 1/true Access Allowed
   * \retval 0/false Access Denied

But in the case no access list exist (accessList = NULL) we have inside
::fastCheck():

     currentAnswer(ACCESS_DENIED);
     while (accessList) {
        ....
     }
     return currentAnswer() == ACCESS_DENIED;

In the case no access list defined, it return true ("access allowed").
We should fix the ::fastCheck or its documentation.

2) Bug in ::fastCheck() method
-------------------------------
Now, when the ::fastCheck() called for a second time or third time, the
accessList is NULL always:
    - if not match because list exhausted in first call
    - if match because of the "cbdataReferenceDone(accessList);" line
(src/acl/Checklist.cc line 350).

So a second call of the ::fastCheck() will return access allowed, even
if the initial decision was access denied...

This is not normal (I think it is a bug).
I propose to replace the old ::fastCheck() method with the new
::reusableFastCheck() code so the fastCheck() calls have simpler
semantics and are always reusable.