more unit tests and javadocs

src/main/java/net/floodlightcontroller/core/SwitchDriverSubHandshakeAlreadyStarted.java

 package net.floodlightcontroller.core;
 
+/**
+ * Thrown when IOFSwitch.startDriverHandshake() is called more than once.
+ * @author gregor
+ *
+ */
 public class SwitchDriverSubHandshakeAlreadyStarted extends
     SwitchDriverSubHandshakeException {
     private static final long serialVersionUID = -5491845708752443501L;

src/main/java/net/floodlightcontroller/core/SwitchDriverSubHandshakeNotStarted.java

 package net.floodlightcontroller.core;
 
+/**
+ * Thrown when a switch driver's sub-handshake has not been started but an
+ * operation requiring the sub-handshake has been attempted.
+ * @author gregor
+ *
+ */
 public class SwitchDriverSubHandshakeNotStarted extends
     SwitchDriverSubHandshakeException {
     private static final long serialVersionUID = -5491845708752443501L;

src/main/java/net/floodlightcontroller/core/SwitchDriverSubHandshakeStateException.java

+package net.floodlightcontroller.core;
+
+/**
+ * Thrown when a switch driver's sub-handshake state-machine receives an
+ * unexpected OFMessage and/or is in an invald state
+ * @author gregor
+ *
+ */
+public class SwitchDriverSubHandshakeStateException extends
+    SwitchDriverSubHandshakeException {
+    private static final long serialVersionUID = -8249926069195147051L;
+
+    public SwitchDriverSubHandshakeStateException(String msg) {
+        super(msg);
+    }
+}