Splay-tree based Proxy-auth ACLs

Second attempt at the problem.
This time it should be complete (the previous version would bomb when
trying to dump them - I had not noticed that function).

This version also supports case-insensitive usernames.
Please have a look, than apply to HEAD. This alone will
speed up my user-acl checks by two orders of magnitude...

Thanks.

-- 
	/kinkie