Revert "Use WP 3.7 tests for 3.6 and 3.7 tests."

This reverts commit 07be47eced2ab96374b91fbfcaa4182828b7b4f4.

Conflicts:
	tests/bin/install-wp-tests.sh
Add memcached server config to wp-config.php.
Only add memcached servers if not defined already.
Begin migrating base setup to own class.
Move add tests into separate file.
Restructure to only include tests in the tests/tests directory.
Add append tests file.
Add CAS tests to separate file.
Add decrement tests to separate file.
Add delete tests to separate file.
Add fetch tests to separate file.
Break get delayed and get multi into separate files.
Add increment tests to separate file.
Add prepend tests to separate file.
Add replace tests to separate file.
Add set tests to separate file.
Move get.php dependencies to that file.
Change file for remaining tests to 'other.php'.
Add decr method to mirror core WP_Object_Cache method.
Add core cache unit tests to suite.