twPrompt( nRow, nCol, _wPrompt, _wMessage )
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     Displays a MENU PROMPT at specified relative window coordinates.
     In this version, the user is responsible for management of the
     MESSAGE option in the normal manner used by Clipper. We may write
     a replacement for Clipper's _atprompt() at a later date. MENU TO
     and case processing is handled by the user.

     See twMenuTo() for a substitute.

       Arguments:

     The first THREE parameters MUST BE PASSED to use this function.

     nRow, nCol - 'N' Relative Window Coordinates.

     _wPrompt   - 'C' Prompt String.

     _wMessage  - 'C' Message String. At present, messages will be
                      processed by Clipper, which means, of course,
                      that window integrity will be violated if you use
                      them, unless you define a window just to hold
                      your menu messages and twPop() it after getting
                      the choice.

       Return:

     Current window handle.

       Example:

     twPrompt( 4, 6, "Choice 1", "Try This First")

     "Try This First" appears in your SET MESSAGE TO location, if you
     have one set.