fix x11 compositor to use damage events

fix x11 compositor to use damage events

it seems that since the first version of the enlightenment compositor
in e17, damage events in x11 have never been used correctly. using
the event struct members will only give the bounding box/area instead
of the damaged regions; the real regions must be explicitly fetched
from the server

this removes the need for a lot of hacks which were added over the years
to make override windows render correctly, and also probably reduces
rendering overhead slightly