Restore a screen.
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 Syntax

         GT_restScr(<cScr>, [<nTop>], [<nLeft>],
                            [<nBottom>], [<nRight>]) --> lRet

 Arguments:

       <cScr>      -  A string previously returned by saveScr()
       <nTop>      -  Top line of screen area to restore
       <nLeft>     -  Leftmost col. of screen area to restore
       <nRight>    -  Rightmose col. of screen area to restore
       <nBottom>   -  Bottom line of screen area to restore

 Returns:

       lRet          - .T. if the screen is restored

 Description:

       Restore a previously saved screen

       The positioning information is optional and if it is  left
       out the screen will restore  to the postion it was  saved.
       If coordinates  are passed,  they must  represent an  area
       exactly equal to that of the saved screen and in the  same
        proportion otherwise the function will return .F.

 Examples:

 Source: RESTSCR.PRG

 Author:  Andy M Leighton