bind: fix field accessors for Go implemented Java classes

The go_seq_to_refnum function handles its argument object as a Java
object if it doesn't implement Seq.Proxy. Java classes implemented in
Go does not implement Seq.Proxy, but when passing "this" references to
Go, instances must be treated as a Go object.

Use go_seq_to_refnum_go everywhere "this" is passed to Go, which fixes
field accessors and simplifies the method call case.

Change-Id: I3d01c63d7b2081e6344ece431f5e5021a9dd7662
Reviewed-on: https://go-review.googlesource.com/31171
Reviewed-by: David Crawshaw <crawshaw@golang.org>

bind/java/ClassesTest.java

@@ -71,6 +71,11 @@ public class ClassesTest extends InstrumentationTestCase {
 		assertNotNull("RuntimeException", exc);
 	}
 
+	public void testField() {
+		GoRunnable r = new GoRunnable();
+		String f = r.getField();
+	}
+
 	public void testGoObject() {
 		Runnable r = new GoRunnable();
 		r.run();