Function:   nxscan( [<expC>] ) --> array

Synopsis:   Scans a workarea for indexes.

            [<expC>]    optional workarea name; defaults to current
                        workarea.

            a workarea is scanned for open indexes. If a workarea
            is passed as parameter, it will be scanned for all open
            indexes, otherwise the current workarea will be scanned.
            All open indexes are written into an array.

Examples:   allindexes := {}
            allindexes := nxscan( ALIAS() ) && scans current workarea

            -or-

            allindex := nxscan()            && scans current workarea

            -or-

            allindex := nxscan( "NEWAREA" ) && scans workarea "NEWAREA"

            -or-

            AREA := "OTHERS"
            allindex := nxscan( AREA )      && scans workarea "OTHERS"

Returns:    array containing open indexes
            empty array if no index found