Initial patch for file suffix acl

Hi

Some time ago Henrik asked for volunteer to some beginner squid developer task.
Due some time constraint problems (working on my final project), I
couldn't work on
it as I desired. But now I have more time (I hope :) ).

Well, here comes a initial patch against squid-2 HEAD which implements a new acl
type, called 'file_suffix'.
It's quite simple:

acl file_suffix exts .cgi .dll .tar.gz .;exe

Please comment it. It works for me, but real world is wider than my tests :)
I've also made some memory leaks tests with valgrind.

regards
Lucas Brasilino