Cleanup PHP 5.5 handling of execute_data.

With 5.5 we start overwriting zend_execute_ex instead of zend_execute
which changes the way we need to handle zend_excuute_data. By fetching
the "real" execute_data directly in hp_execute_ex and
hp_detect_transaction_ex and passing it into
hp_get_function_name/hp_get_function_argument_summary and
hp_detect_transaction_name we simplify code base by making the version
decision only once