Fixed version for 6.x

I'm using cacherouter on live site (apc, memchache, eaccelerator) so I hit a lot of bugs and notices

I remake some code (cleanups & optimizations):

cacherouter.inc
* changed parameters to cache.inc style
* added comments from cache.inc
* cache_clear_all now uses new delete & flush (flush remove only old & temporary items)

Cache.php
* added check for existence $conf mappings
* lookup & look variables are in-class and sharable
* prefix now stored with '-' sign if is set

CacheRouter.php
* Fixed bug with $map (should be $this->map)
* added check for existence $conf mappings

Engines
db.php
* return 0 as in cache.inc
* overload flush to clean expired

apc memcache xcache
* lookup-keys are shared (for multisite) and now stores $expire param
* get - removed unnecessary unserialization
* set - removed unnecessary serialization, temporary items stored as persistent (clean on flush), lock optimizations
* delete - smart use of wildcards, substr changed to strpos, lock optimizations
* flush clean only temp and expired items

added eAccelerator engine

whole tar.gz attached and cumulative patches