Commit Briefs
INSTALL: set $NPROC on macOS
My MacBook Pro has hw.ncpu=12, so set NPROC=12. Speeds up INSTALL dramatically. Should probably add similar code to other OSes. Also silence rio warning from earlier commit.
INSTALL: don't try to use \b in acme window
R=rsc http://codereview.appspot.com/6734051