fix screendump (Stefano Stabellini)

fix screendump (Stefano Stabellini)

this patch fixes the screendump functionality that was recently broken;
it must be applied *after* PATCH 5, 6 and 7 of the original displaystate
change patch series.
In fact the other patches make much easier to solve the screendump
problem because they make the console switching mechanism more robust.

Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6345 c046a42c-6fe2-441c-8c8c-71466251a162

As adapted by Stefano to qemu-xen-unstable in his posting:
 [PATCH 9 of 13] fix screendump
which also contains several following fixes.