Wimp_CommandWindow
------------------

From Select 1 onward, Wimp_CommandWindow has been extended to provide
information about its current state. This information can be used to
determine whether or not an operation will trigger the display of a command
window.

Under normal circumstances, when a task is started by the Window Manager the
command window is marked as 'pending'. In this state, any output to the
screen through the standard VDU calls will cause the command window to be
opened; the state will then be set to 'open'. If the task registers with the
Window Manager with Wimp_Initialise however, the command window is marked is
'inactive'. These states can be changed through the use of
Wimp_CommandWindow as described in the PRMs.

The new call allows clients to identify what state the command window is
currently in.

Wimp_CommandWindow
=> R0 = 2 (Read state)
<= R0 = 0 if the command window is inactive
        1 if the command window is pending
        2 if the command window is open

This SWI is used to find the state of the command window.
