Needed in all scripts that serve binary content or strict XML.
- disable_debugging() - it did not work much because trigger_error was getting to output
- MOODLE_SANE_OUTPUT which was a bit confusing for most devs except ML, it was altering our magic quotes too which might cause major problems in our libs
- various $CFG->debug hacks - CFG should not be modified on the fly
The name was derived from $CFG->debugdisplay - the NO_DEBUG_DISPLAY overrides this setting when debug & errors do not make much sense in output