Squid-2.6 task

One task for Squid-2.6:

We seriously need to clean up peer selection. The current code is quite
messy, somewhat ineffective, very inflexible and generally hard to
understand for our poor users.

From a functionality point of view the biggest drawback is that only one
parent can be selected. This is not what we want when never_direct allow
is in effect. When never_direct is used many of the selection schemes
should return a priority sorted list of peers.

The next functionality drawback is that it is almost impossible for our
users to understand how/why the different selection algorithms and
backup methods goes together. Finding a solution to this is quite likely
a much more complex task than the above..

--
Henrik