[ticket/13280] Properly format the current page and add sanitizer to tests

PHPBB3-13280
[ticket/13280] Correctly format user page for build_url()

PHPBB3-13280
[ticket/13280] Add additional sanitizer for ampersands in server superglobal

PHPBB3-13280
[ticket/13280] Seperate server sanitizer call and add comment

PHPBB3-13280
[ticket/13280] Only run sanitizer for server superglobal and modify tests

PHPBB3-13280
[ticket/13280] Remove unneeded str_replace in build_url()

PHPBB3-13280
Merge pull request #3107 from marc1706/ticket/13280

[ticket/13280] Properly format the current page and add sanitizer to tests

* marc1706/ticket/13280:
  [ticket/13280] Remove unneeded str_replace in build_url()
  [ticket/13280] Only run sanitizer for server superglobal and modify tests
  [ticket/13280] Seperate server sanitizer call and add comment
  [ticket/13280] Add additional sanitizer for ampersands in server superglobal
  [ticket/13280] Correctly format user page for build_url()
  [ticket/13280] Properly format the current page and add sanitizer to tests
[ticket/13295] Add function get_preg_expression() core event

Add function get_preg_expression() core event in includes/functions.php
to allow adding/modifying commonly used regular expresiions.

PHPBB3-13295