[296/906] Fix callbacks passed over XEvents on 64 bit architectures

[296/906] Fix callbacks passed over XEvents on 64 bit architectures

Althought the XEvent's xclient.data.l array is an array of
longs they will be constrained to 32 bit by the X11 protocol.
On 64 bit architectures use two elements of the array to store
one pointer.
This fixes segfaults that happen at least for every example
on startup.