Migrate to GNU General Public License Version 3.

    * COPYING: Replaced with the plain text version of GPLv3.

    * config.guess: Updated from gnulib.
    * config.sub: Likewise.

    * geninit.sh: Output a GPLv3 copyright notice.
    * geninitheader.sh: Likewise.
    * genmodsrc.sh: Likewise.
    * gensymlist.sh.in: Likewise.

    * boot/i386/pc/boot.S: Upgraded to GPLv3.
    * boot/i386/pc/diskboot.S: Likewise.
    * boot/i386/pc/pxeboot.S: Likewise.
    * commands/blocklist.c: Likewise.
    * commands/boot.c: Likewise.
    * commands/cat.c: Likewise.
    * commands/cmp.c: Likewise.
    * commands/configfile.c: Likewise.
    * commands/echo.c: Likewise.
    * commands/help.c: Likewise.
    * commands/ls.c: Likewise.
    * commands/search.c: Likewise.
    * commands/terminal.c: Likewise.
    * commands/test.c: Likewise.
    * commands/videotest.c: Likewise.
    * commands/i386/cpuid.c: Likewise.
    * commands/i386/pc/halt.c: Likewise.
    * comman...