Refactor writing and deleting cache

Should be safe from race conditions an exception now
Save timestamp when removing component cache entry

Simplifies Api
Make Kwf_Component_Cache_Mysql_Test runnable when no memcache is installed
Use string as microtime

To support 32bit systems because integer of timestamp+milliseconds is too large
Get microseconds correctly also when start with 0
Return timestamp, not masked timestamp
Merge pull request #119 from fraxachun/3.4-viewcache-delete

Refactor writing and deleting cache

Should be safe from race conditions and exceptions now