add classes and methods needed for GNU Classpath compatibility

Most of these methods are stubs which throw
UnsupportedOperationExceptions for now.

classpath/java/lang/StringBuilder.java

@@ -10,7 +10,7 @@
 
 package java.lang;
 
-public class StringBuilder implements CharSequence {
+public class StringBuilder implements CharSequence, Appendable {
   private static final int BufferSize = 32;
 
   private Cell chain;
@@ -54,6 +54,14 @@ public class StringBuilder implements CharSequence {
     }
   }
 
+  public StringBuilder append(CharSequence sequence) {
+    return append(sequence.toString());
+  }
+
+  public Appendable append(CharSequence sequence, int start, int end) {
+    return append(sequence.subSequence(start, end));
+  }
+
   public StringBuilder append(char[] b, int offset, int length) {
     return append(new String(b, offset, length));
   }
@@ -150,6 +158,10 @@ public class StringBuilder implements CharSequence {
     return this;
   }
 
+  public StringBuilder insert(int i, CharSequence s) {
+    return insert(i, s.toString());
+  }
+
   public StringBuilder insert(int i, char c) {
     return insert(i, new String(new char[] { c }, 0, 1, false));
   }
@@ -332,4 +344,8 @@ public class StringBuilder implements CharSequence {
     deleteCharAt(index);
     insert(index, ch);
   }
+
+  public void ensureCapacity(int capacity) {
+    // ignore
+  }
 }