The SHOW_EDITOR procedure displays a user-named editor at
the specified display coordinates.
SHOW_EDITOR takes message_in and message_out parameters
that allow you to pass a text string in to the editor and to get the edited
text string back when the operator accepts the editor.
SHOW_EDITOR(editor_name, message_in, x, y, message_out,
result);
The result parameter is a BOOLEAN IN OUT parameter. If
the operator accepts the editor, SHOW_EDITOR sets result to TRUE, and sets
message_out to the current text string. If the operator cancels the editor,
SHOW_EDITOR sets result to FALSE and sets message_out to NULL.
