Add java.lang.Double#doubleToLongBits

It is different than #doubleToRawLongBits only when the input value
is not a number.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>

classpath/java/lang/Double.java

@@ -96,6 +96,11 @@ public final class Double extends Number {
     }
   }
 
+  public static long doubleToLongBits(double value) {
+    if (isNaN(value)) return 0x7ff8000000000000L;
+    return doubleToRawLongBits(value);
+  }
+
   public static native int fillBufferWithDouble(double value, byte[] buffer,
                                                 int charCount);