target-i386: do not override nr_cores for "-cpu host"

Commit 787aaf5 (target-i386: forward CPUID cache leaves when -cpu host is
used, 2013-09-02) brings bits 31..26 of CPUID leaf 04h out of sync with
the APIC IDs that QEMU reserves for each package.  This number must come
from "-smp" options rather than from the host CPUID.

It also turns out that this unsyncing makes Windows Server 2012R2 fail
to boot.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
ui/vnc: optimize clearing in find_and_clear_dirty_height()

using bitmap_clear speeds up for wide areas siginificantly.

Signed-off-by: Peter Lieven <pl@kamp.de>