Bug 2051: 'default' cache_peer option does not match documentation

Bug 2051: 'default' cache_peer option does not match documentation

Move the default parent to second-lowest priority on the parent
selection. This also allows the other more delicate balancing
algorithms to work properly with a default configured.

sourcehash and userhash are reversed in priority to simplify the
selection code around #if..#endif once default is moved.

Also, getAnyParent() is dropped. It is redundant with the FIRSTUP
 algorithm.