cache 6.x-1.0-alpha4

- several fixes when cache chaining is enabled
- fixed page_cache_fastpath() implementation: 304 header now works properly
- changed package group from "Cache" to "Caching" to match boost, pathcache, memcache modules

The following problems of CacheRouter module where fixed (tested or found them already fixed) in this release of Cache module:

#370769: How to use eAccelerator for cache router
#458490: Memcache and Cacherouter status
#434890: encoding break when using file engine.
#533696: memory based cache that supports cache_clear_all wildcard??
#384536: Engine "file": "Failed to create directory"
#463758: Cache Router » package name
#531196: file engine does not work on Window
#347717: File Engine - Add valid file name checking to key generation (Specifically the $appendix)