R_UpdBar() 
 Updates an opened progress bar
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 Syntax
        R_UpdBar ( aBar, nPercentage )

 Arguments
        aBar            Opened progress bar (opened by R_OpnBar())

        nPercentage     Percentage that should be displayed (0-100%)

 Returns
        .T.             Returns always .T. : you can use this function
                        in a WHILE clause of a command.
                        For example :
                        COPY TO Test WHILE R_UpdBar(aBar,100*RecNo()/nRecs)

 Description
        Updates an opened progress bar.
        Pass the percentage of the process that is completed (nPercentage).

 Example
        See the example of R_OpnBar () and the demo program RBarDemo.PRG.