Fix custom login cookies
Fix custom login cookies

I've no idea when this would actually be needed, but at least it should be fixed now.. It broke during the move to use the requests library.

mwclient/mwclient,ubibene/mwclient,danmichaelo/mwclient,JeroenDeDauw/mwclient,PierreSelim/mwclient,AdamWill/mwclient