Tweaks to make libthread tell Valgrind about its stack limits, so that Valgrind can detect stack overflow for me.

clean up when finished. don't set PLAN9 don't set PLAN9

Fighting the good fight. 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.

various tweaks.

make -> mk remove clumsy stack hack. fix exec. fix nthreads maintenance. fix threadexitsall not to kill self. add sun support.