HTTP response splitting in CGI

If an application that generates HTTP responses using the cgi gem with untrusted user input, an attacker can exploit it to inject a malicious HTTP response header and/or body.

Also, the contents for a CGI::Cookie object were not checked properly. If an application creates a CGI::Cookie object based on user input, an attacker may exploit it to inject invalid attributes in Set-Cookie header. We think such applications are unlikely, but we have included a change to check arguments for CGI::Cookie#initialize preventatively.