Because many clients (e.g. termite) prevent us (maybe unknowingly) from
capturing motion events on their windows, we're forced to create a
window for this sole purpose.
Grabbing the pointer isn't an option, because it forces us to consider
some of the enter notify events we should be ignoring.
It appears that unmapping windows might generate undesirable enter
notify events. It can lead a very nasty bug where the focus constantly
switches between two desktops ad infinitum (cf. #268).
Example: if one chromium window is opened and a link is opened in
newsbeuter then chromium will steal the input focus (without explicitly
requesting focus via the proper EWMH message).
The above message was only needed for ending the `move` pointer action
on a floating window. It rendered the `move` pointer action finicky
because the floating rectangle of the floating windows was not updated
in real time.
It seems that pointer motion events are not sufficient to enforce
'focus_follows_pointer': some windows grab the pointer and catch those
events (e.g.: *zenity*), preventing *bspwm* from receiving them. So we
need to listen to enter notify events too.
When the mouse button was released the window under the pointer was
considered as being the window being previously moved. This is false in
the general case and therefore, the window stored inside the
frozen_state variable must be used.
