[ticket/security-164] Sanitize all global variables in symfony_request class

SECURITY-164
[ticket/security-164] Correctly format page_name

SECURITY-164
[prep-release-3.1.1] Add 3.1.1 CHANGELOG
[ticket/13271] Disable CC sender feature for anonymous users

PHPBB3-13271
Merge branch 'ticket/13271' into prep-release-3.1.1

* ticket/13271:
  [ticket/13271] Disable CC sender feature for anonymous users
Merge remote-tracking branch 'github-security/ticket/security-164-alt' into prep-release-3.1.1

* github-security/ticket/security-164-alt:
  [ticket/security-164] Correctly format page_name
  [ticket/security-164] Sanitize all global variables in symfony_request class