added unit test for lfda model

[terrytangyuan]

I added the tests for lfda model. The following gives error:

> train(Class~., data=tr_dat, method="lfda")
Error in train.default(x, y, weights = w, ...) : 
  Model lfda is not in caret's built-in library

I am able to run lfda() or lfda.default() successfully but not through train() as seen above. Do you know how to include the model to the built-in library?

Thanks,
Yuan