JAVA-621: added hashCode()

Author: Steve Briskin

src/main/org/bson/types/BSONTimestamp.java

@@ -59,7 +59,7 @@ public int getInc(){
     public String toString(){
         return "TS time:" + _time + " inc:" + _inc;
     }
-
+    
     @Override
     public int compareTo(BSONTimestamp ts) {
         if(getTime() != ts.getTime()) {
@@ -70,6 +70,15 @@ public int compareTo(BSONTimestamp ts) {
         }
     }
 
+    @Override
+    public int hashCode() {
+        final int prime = 31;
+        int result = 1;
+        result = prime * result + _inc;
+        result = prime * result + getTime();
+        return result;
+    }
+    
     @Override
     public boolean equals(Object obj) {
         if (obj == this)