Updated the JavaDoc for fieldnameprefix.

Author: Denis Nelubin

core/src/main/java/com/yahoo/ycsb/workloads/CoreWorkload.java

@@ -58,6 +58,7 @@
  * <LI><b>maxscanlength</b>: for scans, what is the maximum number of records to scan (default: 1000)
  * <LI><b>scanlengthdistribution</b>: for scans, what distribution should be used to choose the number of records to scan, for each scan, between 1 and maxscanlength (default: uniform)
  * <LI><b>insertorder</b>: should records be inserted in order by key ("ordered"), or in hashed order ("hashed") (default: hashed)
+ * <LI><b>fieldnameprefix</b>: what should be a prefix for field names, the shorter may decrease the required storage size (default: "field")
  * </ul> 
  */
 public class CoreWorkload extends Workload