API request: add a hook prior to classloader detect changes

[bran]

For plugins to implements some java source code engineering, I'd ask for some extra API for the PLayPLugin. Something in the line of:

Would be nice to have this in the next 1.0 series.

public abstract class PlayPlugin2 extends PlayPlugin {
    public abstract void preDetectChanges();
}

And then in the Play.java, modify the detectChanges() to :

   public static synchronized void detectChanges() {
        if (mode == Mode.PROD) {
            return;
        }

       try {
          for (PlayPlugin plugin : plugins) {
           if (plugin instanceof PlayPlugin2) {
            ((PlayPlugin2)plugin).preDetectChanges();
           }
          }
           classloader.detectChanges();
 //.....
        } catch (PlayException e) {
           throw e;
        } catch (Exception e) {
            // We have to do a clean refresh
            start();
        }
    }