[ticket/12071] Skip tests that depend on fileinfo and fix expected results

Tests that depend on fileinfo being enabled will now be skipped to prevent
fatal errors while running the test suite. The expected results will be
modified to "application/octet-stream" in test_guess_files() if only the
extension_guesser is available due to the non-existing extension of those
files.

PHPBB3-12071
[ticket/12071] Get rid of unneeded cast to boolean in tests

PHPBB3-12071
[ticket/12071] Add test that covers not available fileinfo

The newly added test case will also emulate a non-existing fileinfo
in order to check if the mimetype guesser is properly working when
fileinfo is not available.

PHPBB3-12071
[ticket/12254] Better language switching on registration page

PHPBB3-12254
[ticket/12254] Stop using deprecated request_var in user class

PHPBB3-12254
[ticket/12254] Use new set_lang var to avoid conflict with change_lang

PHPBB3-12254
[ticket/12254] Add set_lang var changes to subsilver2 files

PHPBB3-12254
[ticket/12254] Persist set_lang after reg only if changed from default

PHPBB3-12254
[ticket/12254] Use 'language' instead of 'set_lang' as the variable name

PHPBB3-12254
[ticket/12254] No longer need to add change_lang to the URL params

PHPBB3-12254
[ticket/12265] Simplify contact icon design and move to dropdown.

PHPBB3-12265
[ticket/12265] Remove ugly logic.

PHPBB3-12265
[ticket/12265] Fix issue with dropdown being restricted by the width of parent

PHPBB3-12265
[ticket/12265] Add contact icon and remove border from last row & cells.

PHPBB3-12265
[ticket/12265] Ensure that there's only 4 icons per row in IE & Opera.

PHPBB3-12265
[ticket/12265] Adjust alignment of AIM and Jabber icons.

PHPBB3-12265
[ticket/12265] Fix modulo logic.

PHPBB3-12265
[ticket/12265] Break the icons that aren't in loop in case extensions add more

PHPBB3-12265
[ticket/12265] Define a loop for contact icons.

PHPBB3-12265
[ticket/12265] Ensure that dropdown is always at the very left of the container

PHPBB3-12265