Handle multiple 'path' values for Cookie

closes #16 "Rack::Test::CookieJar cannot handle multiple 'path' values in the Cookie."

However this is not a valid cookie string, I've found some web servers that ignore this and still deliver multiple keys. 

http://www.w3.org/Protocols/rfc2109/rfc2109

4.2.2  Set-Cookie Syntax

    ... If an attribute appears more than once in a cookie, the behaviour is undefined. ...