Don't wait for X to finish starting if it has died

On my setup, when X first starts there aren't any screens available so it immediately dies. Half a second later, screens become available but xinit would still be waiting for the dead X process to signal that it is ready. It'll take 15s for it to timeout and respawn X.

This patch makes xinit listen for its child's death and if X dies, it'll immediately stop waiting for it to finish starting and attempt to start it again.