refactoring about caching for php-shindig

I found that there are a few problems when implementing limited invalidation:

1. fix unittest failed

2. fix SHINDIG-926
https://issues.apache.org/jira/browse/SHINDIG-926

3. current caching method put all data into one cache.
I would like to adding name to distinguish each caches. For CacheFile, name is
the directory of cache file. For CacheApc and CacheMemcache, name is the prefix
of keys.

New change:

1. We can't use Apc/Memcache's expiring method because we may need stale
content.
So I stored ttl for Apc/Memcache just like CacheFile.

2. Add invalidate for cache.

[panjie.pan, 2009-03-06 08:59:26]

updated and added unittest for class BasicRemoteContent.