Replace asprintf() with snprintf() in vnc.c ("Daniel P. Berrange")

As previously discussed, this patch removes the non-portable use of
asprintf(), replacing it with malloc+snprintf instead

   Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>


git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6843 c046a42c-6fe2-441c-8c8c-71466251a162
