add a few classes and methods to the classpath

Add java.lang.CharSequence, java.util.AbstractSet,
java.util.AbstractCollection, Collections.unmodifiableSet,
 System.getProperty(String,String), etc.

classpath/java/lang/CharSequence.java

@@ -0,0 +1,11 @@
+package java.lang;
+
+public interface CharSequence {
+	public char charAt(int index);
+	
+	int length();
+	
+	CharSequence subSequence(int start, int end);
+	
+	String toString();
+}