Shorten behavior methods.

Use 5.4 features to make methods shorter. Stop accessing _config
directly and instead use the getter method. If anyone modifies the
behavior of config() we should respect those changes.
Fix behavior method alias management.

When behaviors explicitly defined their finders/methods aliasing and
disabling methods no longer worked. This was due to the underlying
config() method always merging and the values - not the keys - being the
key feature of the data. This new code now uses the values to determine
what the correct config data should be. This results in additional calls
to config when methods are customized, but the code behaves as most
people would expect now.

Refs #4414
Fixing CS error
Fixing another CS error
Merge pull request #4420 from cakephp/issue-4414

Fix broken behavior configuration