phpBB already had limited support for partial downloads, but only for
resuming downloads, disregarding any range ending before EOF.
WebKit on iOS and OS X uses partial downloads when fetching media
files. Previously, only MP3 attachments could play directly in the
browser, reported as a live stream, but with this change, all
supported media formats should render as expected.
Tested using cURL by verifying that partial downloads give exactly the
same results compared to Apache.
PHPBB3-14774
Extend the request class with helpers for reading server vars (server())
and HTTP request headers (header()). Refactor the existing code base
to make use of these helpers, make $_SERVER a deactivated super global.
Also introduce an is_ajax() method, which checks the X-Requested-With
header for the value 'XMLHttpRequest', which is sent by JavaScript
libraries, such as jQuery.
PHPBB3-9716
