Refactored the krr_trainer into two objects. A rr_trainer which just does

linear ridge regression and the krr_trainer which uses the empirical_kernel_map
to do non-linear ridge regression.  No changes were made to the behavior of the
krr_trainer.  This update is just to allow the use of linear ridge regression
without a superfluous empirical_kernel_map running at the beginning of the training
process.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%404114