moved MLP-related costs to pylearn2.costs.mlp
make preprocessor not run if data wasn't loaded
give MLP a default_cost method
add deprecation warning messages for old import locations
gave the Model a get_default_cost method
partial cleanup of deep_trainer
make BGD and SGD accept None as the cost argument
Merge branch 'master' of github.com:lisa-lab/pylearn2

Conflicts:
	pylearn2/datasets/mnist.py
updated tutorials to use the new mlp.WeightDecay location
moved a cell that was in the wrong place
Merge pull request #209 from goodfeli/master

better organization of MLP costs