default RegionScanner postScannerOpen(ObserverContext<? extends RegionCoprocessorEnvironment> c,
    Scan scan, RegionScanner s) throws IOException {
    return s;
  }
Called after the client opens a new scanner.
<p>
Note: Do not retain references to any Cells returned by scanner, beyond the life of this
invocation. If need a Cell reference for later use, copy the cell and use that.
@param c    the environment provided by the region server
@param scan the Scan specification
@param s    if not null, the base scanner
@return the scanner instance to use
hbase-server/src/main/java/org/apache/hadoop/hbase/coprocessor/RegionObserver.java