fixing edge case error caused when the headers object contained a 'hasOwnProperty' property.
fixing edge case error caused when the headers object contained a 'hasOwnProperty' property.

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