[ticket/13052] Restore timespan parameter for check_form_key()

PHPBB3-13052
Merge pull request #2939 from nickvergessen/ticket/13052

[ticket/13052] Restore timespan parameter for check_form_key()

* nickvergessen/ticket/13052:
  [ticket/13052] Restore timespan parameter for check_form_key()
Merge branch 'develop-ascraeus' into develop

* develop-ascraeus:
  [ticket/13052] Restore timespan parameter for check_form_key()