* 3.1.x:
[ticket/security-180] Use language variable for redirect error in 3.1+
[ticket/security-180] Merge if statement with previous one in 3.1.x
[ticket/security-180] Add tests for redirecting to main URL
[ticket/security-180] Always fail when redirecting to an insecure URL
[ticket/security-180] Make sure that redirect goes to full URL plus slash
[ticket/security-180] Check if redirect URL contains board URL