to an actual flag. buffer underrun check in number add xdata file for exactly the addressed region save addr across opens

More changes.

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.