Function:    MouseSet()

               .t. by default, The mouse can be set OFF at all times
               by selecting MouseSet(.f.). This van be handy when one
               explicitly does not want to use the Mouse.
               When MouseSet() is set OFF (.f.), MouseThere() will always
               return .f., by which it seems there is no mouse. When
               MouseSet() is ON (.t.), MouseThere() returns .t. when a Mouse
               is installed.
               MouseSet() in ON by default.

  Syntax:      MouseSet([lMouse]) --> lMouseSetting

  Arguments:   .t. Indicates that you would want to use the Mouse if
               present. .f. indicates NO, NO MOUSE!

  Returns:     The current setting of MouseSet().

  Usage:       You may want to leave it to the user, in the Options menu
               of you application, to decide whether (s)he wants a Mouse when
               available.