private Double decodeDouble(byte[] in) {
    assert in.length == 9 : "Wrong length for a double";
    Long l = decodeLong(in);
    return Double.valueOf(Double.longBitsToDouble(l.longValue()));
  }
Handles old whalin (tested with v1.6) encoding: data type is in the first
byte of the value.

@author bpartensky
@since Oct 16, 2008
src/main/java/net/spy/memcached/transcoders/WhalinV1Transcoder.java