Add skeleton for string library calls.

src/main/java/lua/VM.java

@@ -146,4 +146,11 @@ public interface VM {
 	 * must be on the top of the stack.
 	 */
 	public void lua_error();
+
+	/**
+	 * Raises an error.   The message is pushed onto the stack and used as the error message.  
+	 * It also adds at the beginning of the message the file name and the line number where 
+	 * the error occurred, if this information is available. 
+	 */
+	public void luaL_error(String message);
 }

src/main/java/lua/debug/DebugStackState.java

@@ -7,7 +7,6 @@ import java.util.StringTokenizer;
 import lua.CallInfo;
 import lua.StackState;
 import lua.io.LocVars;
-import lua.value.LValue;
 
 public class DebugStackState extends StackState implements DebugRequestListener {
 	
@@ -18,7 +17,6 @@ public class DebugStackState extends StackState implements DebugRequestListener
 	private int lastline = -1;
 	
 	public DebugStackState() {
-		StackState.debugHooksEnabled = true;
 	}
 	
 	// debug hooks

src/main/java/lua/value/LString.java

@@ -342,4 +342,8 @@ public class LString extends LValue {
 		System.arraycopy( a, 0, newbytes, 0, Math.min( newSize, a.length ) );
 		return newbytes;
 	}
+
+	public int luaByte(int index) {
+		return m_bytes[m_offset + index];
+	}
 }