Add in the ability to launch non xsbti.AppMain classes.

* Deprecate old mainClass method on appProvider
* Create entryPoint method which represnets class used to launch instead.
* Create PlainApplication to wrap static `main` methods.  Can return
  either Int, Exit or Unit.
* Detect supported 'plain' classes via reflection.
* Add new unit tests appropriate to the feature.

launch/interface/src/main/java/xsbti/AppProvider.java

@@ -8,13 +8,27 @@ public interface AppProvider
 	public ScalaProvider scalaProvider();
 	/** The ID of the application that will be created by 'newMain' or 'mainClass'.*/
 	public ApplicationID id();
-
-	 public ClassLoader loader();
-	/** Loads the class for the entry point for the application given by 'id'.  This method will return the same class
-	* every invocation.  That is, the ClassLoader is not recreated each call.*/
+	/** The classloader used to load this application. */
+	public ClassLoader loader();
+	/** Loads the class for the entry point for the application given by 'id'.  
+	 * This method will return the same class every invocation.  
+	 * That is, the ClassLoader is not recreated each call.
+	 * @deprecated("use entryPoint instead")
+	 * 
+	 * Note:  This will throw an exception if the launched application does not extend AppMain.
+	 */
+	@Deprecated
 	public Class<? extends AppMain> mainClass();
+	/** Loads the class for the entry point for the application given by 'id'.  
+	 * This method will return the same class every invocation.  
+	 * That is, the ClassLoader is not recreated each call.
+	 */
+	public Class<?> entryPoint();
 	/** Creates a new instance of the entry point of the application given by 'id'.
-	* It is guaranteed that newMain().getClass() == mainClass()*/
+	* It is NOT guaranteed that newMain().getClass() == mainClass().
+	* The sbt launcher can wrap generic static main methods. In this case, there will be a wrapper class,
+	* and you must use the `entryPoint` method.
+	*/
 	public AppMain newMain();
 	
 	/** The classpath from which the main class is loaded, excluding Scala jars.*/