Commit Briefs
libthread: run first thread in proc on system stack
For pthread systems that are fussy about which stack is used, this makes sure that threadmain runs on a system stack. If you only use proccreate (never threadcreate), all threads run on system stacks.
libthread: add threadspawnd
R=rsc http://codereview.appspot.com/6742064
Rewrite page(2) references to page(3).
Add description of new libmach.