Issue #2455: Make RBM work with sparse input when verbose=True.
Change RBM sparse format from CSC to CSR.
Cosmetic changes.
Add issparse import.
Cosmetic changes.
Expanded docstring of the verbose parameter.
Check that verbose output is sound.
Merge pull request #2457 from untom/rbm_csr_format

[MRG] Switch BernoulliRBM to CSR format