MetaIdleMonitorDBus: unref the objects after exporting them

The object manager already has a reference.

https://bugzilla.gnome.org/show_bug.cgi?id=729732
MetaDisplay: free the wayland windows table at close

Like we do for the XID table.

https://bugzilla.gnome.org/show_bug.cgi?id=729732
default: free the option context after parsing

We don't need it, we should free it.

https://bugzilla.gnome.org/show_bug.cgi?id=729732
MetaStackTracker: make sure all stack ops are freed eventually

If we apply a prediction immediately instead of queueing, we should
also free the operation immediately.
If we discard the prediction queue because we resync fully, we
need to free each operation too.

https://bugzilla.gnome.org/show_bug.cgi?id=729732
xprops: free the text list content too

A text list is an array of pointers into a buffer. Freeing the
array is not enough, we need to free the buffer too.

https://bugzilla.gnome.org/show_bug.cgi?id=729732