Tests for covering the Doctrine_Collection::loadRelated functionality for basic many-to-many relations

By default mysql connection doesn't use DQL record limit (it doesn't support limit in subqueries yet)

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* Added some test cases for the importing part. The new tests will fail for now because of the lacking implementation.
Refs #11 

Fixed Doctrine_Record::exists() and removed final attribute since its *not* a method that is used by Doctrine internally

Added exists() to check for existence of data, getColumnCount() as alias to count() and renamed has() to hasRelation() for clarity

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