bump(app-emulation/qemu): sync with upstream

Our current version, 1.2, is quite old. Bump to the latest stable (1.4)
with an eye towards bumping to 1.5 as soon.

Packages updated:
  app-emulation/qemu
  sys-firmware/ipxe
  sys-firmware/seabios
  x11-libs/pixman
Merge pull request #33 from marineam/qemu

bump(app-emulation/qemu): sync with upstream