Set con window to NULL on tree_close

Prevents invalid reads on the freed window struct.
Update ipc library list documentation

Add a link to the new JavaScript, Python, and Lua ipc libraries.

Add notice that the older Python libraries are not maintained.

Sort the list alphabetically.
Free window ran_assignments on tree_close
Add valgrind suppression file to testcases

The suppression file makes valgrind output more readable by hiding
reports of memory leaks for GObject-related initialization functions in
Pango and Cairo.
Merge branch 'next' of git://code.i3wm.org/i3 into next

Conflicts:
	src/tree.c