clean up argument parsing.

various other little fixes.

Lots of new code imported.

Move libfmt, libutf into subdirectories of lib9. Add poll-based socket i/o to libthread, so that we can avoid using multiple procs when possible, thus removing dependence on crappy pthreads implementations. Convert samterm, acme to the single-proc libthread. Bring libcomplete, acme up-to-date w.r.t. Plan 9 distribution.

which were completely bogus. (Libthread used to ignore them but not anymore. Maybe we really should ignore them, but that breaks Venti, which needs *really* big stacks.)