Handle SDL grabs failing (Mark McLoughlin)

Handle SDL grabs failing (Mark McLoughlin)

If a X window is not viewable, XGrabPointer() fails and
returns GrabNotViewable. SDL's X backend currently handles
this by retrying the grab until the window becomes viewable
again.

This means e.g. if you Ctrl-Alt-RightArrow to switch
workspaces, QEMU tries to grab, SDL blocks because the
window isn't viewable and your guest stops executing until
you switch back to that workspace again.

See this Fedora bug for the gory details:

  https://bugzilla.redhat.com/480065

Some SDL backends will return SDL_GRAB_OFF from
SDL_WM_GrabInput(), so the fix is to make the X backend do
this if the grab fails.

The only side-effect in QEMU is that if SDL_WM_GrabInput()
fails we still change the window title to indicate that it's
grabbed, when in fact it's not. This patch fixes that minor
issue.

Signed-off-by: Mark McLoughlin <markmc@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@6325 c046a42c-6fe2-441c-8c8c-71466251a162