just copy over the source URL and other relevant fields (to avoid copying event handlers). r=bzbarsky, sr=jag, a=valeski. Patch by jrgm@netscape.com. git-svn-id: svn://10.0.0.236/branches/MOZILLA_1_0_BRANCH@124219 18797224-902f-48f8-a5cc-f745e15eee43