xwm leaves zombie processes

[vainiovano]

xwm doesn't wait the exit statuses of the processes that it creates. When a process created by xwm exits, it's left as a zombie until it's are reaped by init when xwm is closed.

[mcpcpc]

#12 should now address this and properly reap zombie processes. Messing around with alternative options at the moment (e.g. double fork), so I will most likely hold off merging for a day or two.

edit: I will most likely proceed with the "double fork" method since the signal.h library is arguably not preferred (as it contains implementation-defined and undefined behavior).