Fix EZP-23296: Template Block Cache has cache key collisions

The template cache blocks where using crc32 which has a high probability of collisions.
Feature has been changed to use md5 like viewcache already uses.

Note: To avoid that you have to many cache blocks take advantage of putting identical once in
own templates so they will share the case (file and location of block is part of the unique key).

If this is back ported to 5.3, additional note about cache blocks having to cleared should be added.
Typo :-)