cirrus vga is very slow in qemu-kvm-0.12

As has been reported multiple times (*), there were a regression in qemu-kvm from 0.11 to 0.12, which causes significant slowdown in cirrus vga emulation.  For windows guests, where "standard VGA" driver works reasonable well, -vga std is a good workaround. But for e.g. linux guests, where vesa driver is painfully slow by its own, that's not a solution.

(*)
 debian qemu-kvm bug report #574988: http://bugs.debian.org/574988#17
 debian qemu bugreport (might be related): http://bugs.debian.org/575720
 kvm mailinglist thread: http://<email address hidden>/msg33459.html
 another kvm ml thread: http://<email address hidden>/msg32744.html