Fix check for chunked transfer-encoding
Fix check for chunked transfer-encoding

The Transfer-Encoding header can contain many values separated by
a comma, e.g.,

    Transfer-Encoding: chunked, gzip

If we want to check for chunked transfer encodings we're better off
not looking for equality since the above header value also indicates
a chunked body. Instead, we need to split on ", " to ensure we can
accurately determine if a response is chunked.

luca3m/urllib3,msabramo/urllib3,sornars/urllib3,boyxuper/urllib3,mikelambert/urllib3,sileht/urllib3,Geoion/urllib3,denim2x/urllib3,haikuginger/urllib3,sileht/urllib3,Disassem/urllib3,sigmavirus24/urllib3,tutumcloud/urllib3,gardner/urllib3,tutumcloud/urllib3,urllib3/urllib3,silveringsea/urllib3,matejcik/urllib3,haikuginger/urllib3,sornars/urllib3,luca3m/urllib3,Disassem/urllib3,denim2x/urllib3,matejcik/urllib3,mikelambert/urllib3,gardner/urllib3,msabramo/urllib3,sigmavirus24/urllib3,Geoion/urllib3,boyxuper/urllib3,Lukasa/urllib3,silveringsea/urllib3,Lukasa/urllib3,urllib3/urllib3