Commit Briefs
libthread: add threadmaybackground
Programs that want to background themselves now need to define threadmaybackground returning 1. This avoids a confusing (to people and debuggers) extra parent process for all the threaded programs that will never want to background themselves.
fossil: required p9p changes
R=rsc https://codereview.appspot.com/13352057
fossil: move from liboventi to libthread and libventi
R=rsc https://codereview.appspot.com/13504049
fossil: import from plan 9
R=rsc https://codereview.appspot.com/7988047