RFC prevention.
At the line :711 if URL is to small to check if there is a "http" at the beginning it will just pass without raise an "invalid URL". If it is the case, a regex will detects it. (see the RFC 3986 http://tools.ietf.org/html/rfc3986 or the 1738 http://www.ietf.org/rfc/rfc1738.txt for more information).