finish java/lang/ref/* support; add wrapper classes for primitives

classpath/java/lang/Double.java

@@ -0,0 +1,13 @@
+package java.lang;
+
+public final class Double {
+  private final double value;
+
+  public Double(double value) {
+    this.value = value;
+  }
+
+  public double doubleValue() {
+    return value;
+  }
+}