The intermediate fork needs to wait for SIGUSR1 for when Xserver is
ready, or SIGCHLD if the exec didn't work out.
Also change the exit() to _exit() as that is apparently more appropriate
for forks (and waitpid's status was wrong without it for some reason)
Fixes#122.
This hardcodes a define, but other projects (wlc/weston) either use the raw
number or just redefine it with another name anyway...
This should fix travis build.
handle map/unmap_notify, property_notify (just logging for now), and
client_message for wl_surface_id.
We almost can display an X window now, just need the compositor to
iterate over them