Favor window global over self global
Favor window global over self global

So that Q can be used as a <script> in Firefox add-ons.
The self object does not refer to window and is immutable.

Fixes #631

IlianStefanov/q,100star/q,b12consulting/q,X-Bird/q,pwmckenna/q,greyhwndz/q,ShopCo/q,jymsy/q,CozyCo/q,ajunflying/q,Muffasa/q,kriskowal/q,pwmckenna/q,jymsy/q,ajunflying/q,kriskowal/q,criferlo/q,darkdragon-001/q,miamarti/q,welbornio/q,signpost/q,potato620/q,homer0/q,mcanthony/q,zhangwenquan/q,aramk/q,liwangbest/q,ShopCo/q,X-Bird/q,IbpTeam/node-q,Muffasa/q,aramk/q,linalu1/q,homer0/q,CozyCo/q,b12consulting/q,lidasong2014/q,cgvarela/q,gustavobeavis/q,liwangbest/q,yizziy/q,gustavobeavis/q,miamarti/q,willsmth/q,rasata/q,IbpTeam/node-q,behind2/q,manushthinkster/q,Zeratul5/q,SarunasAzna/q,IlianStefanov/q,welbornio/q,harks198913/q,zhangwenquan/q,dracher/q,darkdragon-001/q,bnicart/q,mcanthony/q,SarunasAzna/q,yizziy/q,rasata/q,behind2/q,manushthinkster/q,harks198913/q,criferlo/q,Zeratul5/q,potato620/q,lidasong2014/q,bnicart/q,dracher/q,greyhwndz/q,willsmth/q,linalu1/q,signpost/q,cgvarela/q