Add missing file to CMakeLists
Discard new resize events when a new one arrives

- We delay some GUI events by posting them into a
  queue - for resize events we now delete old events
  when we get a new one.
Enable console messages for windows Debug builds
Revert to old painting strategy using a pixmap
Call gui_set_shellsize after window resize
Force call to gui_resize_shell() in gui_mch_set_shellsize()

- it seems in cases where gui_resize_shell() is called but
  the shell size actually remains the same, gui_resize_shell() is
  never called, causing Vim to assume it was resized.