Implmented cache group clearing in Memcache engine
Implementing group support for XcacheEngine
Implemented group support in WincacheEngine
Implemented read/write support for groups in FileEngine
Implemented group cache delete in FileEngine
Fixing some typos
Fixing cache group related test cases.
Merge pull request #583 from tPl0ch/2.2-cache-groups

Fixed failing tests for 2.2 cache groups fetaure.
Merge branch '2.1' into 2.2
Start Set2.
Add function prototypes.
Adding dimensions() and maxDimensions()

Splitting the Set::countDim() into two methods.  This creates a simpler
API, as each method only does one job, and only has one argument.  Also
replacing recursion with iteration.
Moving flatten() across.

It is no longer recursive either.
Move merge() into Set2.
Move normalize() into Set2.

Dropping the ability to 'normalize' string data.
Move contains() across.

Fix a few issues in contains() with nested needle values.
Make contains() non-recursive.

Add a few more tests for contains().
Moving filter() into Set2.
Move numeric() into Set2.
Basic path selectors implemented for extract().