The mouse in Linrad is driven from a mouse thread which is
different under Windows, Linux with svgalib and Linux with X11.
With svgalib the mouse thread waits for a return from mouse_update()
which returns each time a mouse event has happened.
Under Windows, mouse events are captured by the callback procedure WndProc
which stores the mouse status and posts to the mouse thread.
The Windows mouse thread waits for the posts from WndProc and then
executes similar code to the one used under Linux.
X11 is similar to Windows.

                          MOUSE MOVES
Mouse moves cause changed values for new_mouse_x and new_mouse_y
The screen thread detects whether mouse_x differs from new_mouse_x
or if mouse_y differs from new_mouse_y. If the mouse has moved,
the screen thread calls lir_move_mouse_cursor() which sets mouse_x = 
new_mouse_x and mouse_y = new_mouse_y. This routine is different
under Linux and Windows. Under Windows it does nothing more while
it removes the old mouse cursor under Linux and sets up some variables
for the new curser position.

                    BUTTON PRESS OR RELEASE
The response to a button state change may affect pointers and memory
allocations in different threads. During normal processing the wideband
thread may respond to both mouse buttons while the narrowband thread
only responds to the left button.

The left button operates like this:
Normal flag status:
   mouse_task=-1   
   leftpressed=BUTTON_IDLE
   mouse_active_flag=0
   mouse_counter=0

Left button pressed: