ENH: svm check for conflict with neuroelf now checks the training function
DOC: update documentation of SVM classification
NF+RF+BF+BK+ACK: update cross-validation and winner_indices to use NaN for missing predictions (rather than 0). Refactoring of winner_indices fixes the issue with missing predictions. Thanks to #James Keidel# and #Jia Hou Poh# for bringing up this issue
RF: use of cosmo_warning, which by default shows each unique warning just once