After reading some PHP source as well as the PHP manual we have arrived at the
following two situations with one conclusion:
* SAPI supports flush():
o call to flush() is enough to stop the page from displaying as loading
o and thus register_shutdown_function is unnecessary
* SAPI does not support flush():
o neither a call to flush() nor the beginning of shutdown phase, which calls
registered shutdown functions can flush anything to the client
o and thus register_shutdown_function is unnecessary
Thanks to lacton for reporting the initial issue.
Thanks to nn- and naderman for doing all the dirty works.
PHPBB3-10046