In non-debug mode, propose:
(In ) fixes #1320 - output tracking pixel at start of request to increase perceived tracker responsiveness
the tradeoff is the loss of some user-readable text in non-debug mode for empty requests and exceptions
(arguably, we probably shouldn't have been outputing e->getMessage() in non-debug mode)
(In ) refs #1320 - comment out obsolete tests; may want to re-enable when we can control PIWIK_TRACKER_DEBUG (e.g., via config setting?)
Nice change for speed!