Reader and Writer are abstract classes. GWT tests work now. Yay!

src/main/java/com/samskivert/gwt/java/io/Reader.java

@@ -6,7 +6,7 @@ package java.io;
 /**
  * A minimal version of {@code Reader} to satisfy GWT.
  */
-public interface Reader
+public abstract class Reader
 {
-    int read () throws IOException;
+    public abstract int read () throws IOException;
 }

src/main/java/com/samskivert/gwt/java/io/StringReader.java

@@ -6,7 +6,7 @@ package java.io;
 /**
  * A basic implementation of {@code StringReader} for use in GWT.
  */
-public class StringReader implements Reader
+public class StringReader extends Reader
 {
     public StringReader (String data) {
         _data = data;

src/main/java/com/samskivert/gwt/java/io/StringWriter.java

@@ -6,7 +6,7 @@ package java.io;
 /**
  * A basic implementation of {@code StringReader} for use in GWT.
  */
-public class StringWriter implements Writer
+public class StringWriter extends Writer
 {
     public void write (String text) throws IOException {
         _buf.append(text);

src/main/java/com/samskivert/gwt/java/io/Writer.java

@@ -6,7 +6,7 @@ package java.io;
 /**
  * A minimal version of {@code Writer} to satisfy GWT.
  */
-public interface Writer
+public abstract class Writer
 {
-    void write (String text) throws IOException;
+    public abstract void write (String text) throws IOException;
 }