Drawing is done via the GDI drawing functions. The cursor is
converted to a monochrome version before drawing. This is because
the GDI drawing functions seem to have undefined behavior with
cursor images including an alpha channel.
I could not find any other reliable way to draw these alpha
channel cursors without producing unwanted artifacts. These type
of cursors were introduced with Window Vista when run with it's
Aero theme.
Also adjust the cursor coordinates when capturing non-primary
screens via the "monitor" option.
https://bugzilla.gnome.org/show_bug.cgi?id=760172
Also implement framerate handling correctly by borrowing the code from
ximagesrc. GstBaseSrc::get_times() can't be used for that, we have to
implement proper waiting ourselves.
