Ecore_X(cb): Enable code for using xprint to get window root list

Ecore_X(cb): Enable code for using xprint to get window root list
(like xlib has). Remove some fixme's (implement error checking for a
few functions).

NB: While this code makes ecore_x_window_root_list work like the xlib
version does (ability to use xprint to get list), I highly recommend
building ecore without xprint support (--disable-ecore-x-xprint)
because this seems like a lot of work to go through to get the window
root list. Building without xprint support provides a faster code path.

git-svn-id: svn+ssh://svn.enlightenment.org/var/svn/e/trunk/ecore@62696 7cbeb6ba-43b4-40fd-8cce-4c39aea84d33