[BUGFIX] Fix for the failing PHPUnit tests in some 3rd party extensions

Improved support for PHPUnit tests by hooking to the PHPUnit bootstrap process
in TYPO3 phpunit extension by overriding default implementation for the
Tx_Phpunit_BackEnd_Module and Tx_Phpunit_TestRunner_CliTestRunner classes.
This way we have more predictable overriding of the database connection
initialization logic.