Previously, we would be limited by the way allParams will return 3 parameters
at most. This way, we get the full URL.
Keep in mind, this code still needs a clean up, but at least it's not buggy now.
Regression from f972466880.
Passes tests in 3.1, but fails in master due to Deprecation notices.
Tests needed adjustments because OldPageRedirector::find_old_page()
doesn't have the same method signature...
