a list of small things to fix for qemu-kvm-0.12.3.1

[Michael Tokarev <mjt@tls.msk.ru>]

..or for subsequent releases.

First of all, roms/{sea,vga}bios directories
are empty in qemu-kvm tarballs but they're
present in qemu tarball.  I think the sources
for the bioses should be restored.

While at it, the EXTERNAL_DEPENDENCIES file
should list actual git commit ID for the
seabios used, which is "two commits ahead
of 0.5.1 release".

And while at it, pc-bios/README should probably
be updated to reference to roms/* as well as
to the original sources for the binaries.  But
that's in qemu.

The following files should be removed when
releasing a new version:

 qemu/pc-bios/extboot.bin
   (this one slipped in from an old directory,
    it's now without first "qemu" component;
   And yes, 0.12.3 tarball has that file for
   some unknown reason).

 git-related files (.gitignore, .gitmodules
   and kvm/.gitignore) should be removed too
   when releasing things, IMHO.

Thanks!

/mjt