Proxy-auth ACLs as splay trees

I've implemented preliminary support to
have Proxy-auth ACLs implemented
as splay trees. This is something
I'd really like to have, as my long ACLs
are, I suspect, quite a burden for my
system.

The attached patch includes such work.
It's still not complete (please have
a look to decide whether it's workable),
as I wish to add support for
case-insensitive usernames-checking, which
I'll work on shortly.

Thanks.

-- 
	/kinkie