Make `origin` header set only if there is not XHR2 API
Make `origin` header set only if there is not XHR2 API

`origin` header is considered unsafe in webkit and there is an error
trying to set `origin` header

chazen/easyXDM,oyvindkinsey/easyXDM,chazen/easyXDM,jmptrader/easyXDM,aaron-goshine/easyXDM,lanson647/easyXDM,jmptrader/easyXDM,aaron-goshine/easyXDM,lanson647/easyXDM,jspath/easyXDM,oyvindkinsey/easyXDM,cake-disposal-squad/easyXDM,oyvindkinsey/easyXDM,cake-disposal-squad/easyXDM,oyvindkinsey/easyXDM,jspath/easyXDM,oyvindkinsey/easyXDM,lanson647/easyXDM,chazen/easyXDM,jspath/easyXDM,aaron-goshine/easyXDM,cake-disposal-squad/easyXDM,jmptrader/easyXDM