When an http response has two Set-Cookie in the header, response['Set-Cookie']
will return a single string. This string will be the two returned cookies
separated by a comma, concatenated together. Instead this should use
get_field('Set-Cookie') which returns an array of returned cookie strings.
The syntax of cookies is described in http://www.ietf.org/rfc/rfc2109.txt,
section 4.1. Cookies are attribute-value pairs, so split should only return 2
values. This will allow '=' within the value of a cookie.
Merge pull request #218 from dwnichols/master

Updating the handling of Set-Cookie in http responses