Allow timeout option for GM_xmlhttpRequest.
Allow timeout option for GM_xmlhttpRequest.

Fixes #1561

the8472/greasemonkey,Ventero/greasemonkey,the8472/greasemonkey,HasClass0/greasemonkey,Martii/greasemonkey,Martii/greasemonkey,HasClass0/greasemonkey,Ventero/greasemonkey