Closes #1007
Closes #1007

Provide an abort() method to GM_xmlhttpRequest calls.

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