Handle comma-seperated Connection header

Specifically in the case of Firefox where the client sends multiple values in a comma-seperated format for the Connection header (ie. "Connection: keep-alive, Upgrade"). This was preventing Firefox (tested on v28) from properly connecting to servies which provide a websocket endpoint, while other browsers (ie. Chrome) were able to connect.

Reference: http://tools.ietf.org/html/rfc2616#section-4.2

Quote:

 Multiple message-header fields with the same field-name MAY be
   present in a message if and only if the entire field-value for that
   header field is defined as a comma-separated list [i.e., #(values)].
   It MUST be possible to combine the multiple header fields into one
   "field-name: field-value" pair, without changing the semantics of the
   message, by appending each subsequent field-value to the first, each
   separated by a comma. The order in which header fields with the same
   field-name are received is therefore significant to the
   interpretation of the combined field value, and thus a proxy MUST NOT
   change the order of these field values when a message is forwarded.