[ticket/11508] Split parts of build_url() into reusable functions.

PHPBB3-11508
[ticket/11508] Build the jumpbox hidden fields using the _form action_

PHPBB3-11508
[ticket/11508] Move the stripping param code to separate function as well.

PHPBB3-11508
[ticket/11508] Move helper functions to path_helper class.

PHPBB3-11508
[ticket/11508] Change separator parameter to a simple true|false $is_amp.

PHPBB3-11508
[ticket/11508] Do not add the '?' unless there are parameters.

PHPBB3-11508
[ticket/11508] Add tests.

PHPBB3-11508
[ticket/11508] The question mark is expected even if there are no parameters.

PHPBB3-11508
[ticket/11508] Curly brace should be on its own line...

PHPBB3-11508
[ticket/11508] Fix build_url test.

PHPBB3-11508
[ticket/11508] Remove unnecessary isset check.

PHPBB3-11508
[ticket/11508] Remove unnecessary implode.

PHPBB3-11508
[ticket/11508] Allow equal sign in parameter value.

PHPBB3-11508
[ticket/11508] Use $phpbb_path_helper.

PHPBB3-11508
[ticket/11508] Add functional test for jumpbox.

PHPBB3-11508
[ticket/11508] Fix build_url test.

PHPBB3-11508
Merge remote-tracking branch 'github-prototech/ticket/11508' into develop-ascraeus

* github-prototech/ticket/11508:
  [ticket/11508] Fix build_url test.
  [ticket/11508] Add functional test for jumpbox.
  [ticket/11508] Use $phpbb_path_helper.
  [ticket/11508] Allow equal sign in parameter value.
  [ticket/11508] Remove unnecessary implode.
  [ticket/11508] Remove unnecessary isset check.
  [ticket/11508] Fix build_url test.
  [ticket/11508] Curly brace should be on its own line...
  [ticket/11508] The question mark is expected even if there are no parameters.
  [ticket/11508] Add tests.
  [ticket/11508] Do not add the '?' unless there are parameters.
  [ticket/11508] Change separator parameter to a simple true|false $is_amp.
  [ticket/11508] Move helper functions to path_helper class.
  [ticket/11508] Move the stripping param code to separate function as well.
  [ticket/11508] Build the jumpbox hidden fields using the _form action_
  [ticket/11508] Split parts of build_url() into reusable functions.