redis 7.x-3.0

This is the first almost stable - yet untested on production environment - of the 3.x version of this module.

Please test it carefully before upgrading on existing production environments. Any kind of feedback is welcome. Beware that the EVAL command as of today makes it non-shardable, solution(s) are still being investigated.

Major changes are mostly internal:

• PhpRedis and Predis code has been dramatically reduced in the flavor of backend agnostic business code for handling all Drupal cache configuration and behavior specifics.
• The module now requires the EVAL command and a few LUA scripts to work, therefore Redis server minimal required version is now 2.6.0 compiled with LUA scripting capabilites. For all users that cannot upgrade, please continue using the 2.x versions which will remain supported and maintained for bugfixes.
• Redis usage should scale a lot better thanks to LUA scripting - you shouldn't experience cache flush problems anymore.
• Default flush modes for bins have changed since the module scales better.

Important other notes:

• Configuration of the module remains backward compatible with 2.x version.
• The flush mode configuration default behavior changes, but won't affect most users. The module is now able to behave exactly like the Drupal database default backend.
• The "flush all" flush mode has been dropped now that all others are considered as safe, if you configured some bins using it they will fallback silently to default behavior.
• A "never flush" mode has been added and explicitely asks the module to never flush entries in Redis and let it proceed with LRU eviction - consistency checks being done at cache fetch time this should be safe to use ; although you should care about this fact this feature is unfinished.
• All unit tests pass nevertheless this new version hasn't been widely tested, any kind of feedback is welcome.