fix cost_from_X_data_specs
fix definition of the 'misclass' channel in Softmax where _has_binary_target
Check that mlp with index targets and vector targets behave the same.

Compare 'misclass' and 'nll' monitoring channels.
Merge pull request #1209 from lamblin/micklat-fix_mlp_softmax_misclass_rebased

Fix mlp softmax misclass and cost_from_X when the top layer is Softmax with binary_target_dim