This was probably necessary all along, and the test happened to work
because state was not correctly reset between test runs and
a previous test set an empty template path.
PHPBB3-10933
A new method to handle this type of path was added and
compile_tag_include, compile_tag_include_php and
compile_tag_include_js were modified to use it appropriately.
Tests were added for these three macros also.
PHPBB3-10970
The template stream filter no longer depends on the $config global.
Instead it uses a 'allow_php' param that is passed via
stream_bucket_append's last argument.
Tests also adjusted.
PHPBB3-9726
