Travis: Initiating build for commit '7f48059f52b807b4e8d2d05ff70279c94e626cc6': Make sure all calls to Piwik_ExitWithMessage provide backtrace if available, and only print the backtrace if PIWIK_PRINT_ERROR_BACKTRACE is defined. Modified archive cron test to print backtrace if request made by archive cron test fails.