destructively aliased its second argument.
 - Moved matrix_exp into its own file
 - Removed all the operator templated matrix expression classes from matrix_expressions.h
   and replaced them with a single (much simpler) class called matrix_op.  This new
   class is located in matrix_op.h.   Virtually all the code changes in this commit are just
   the refactoring needed to support this change.  No functionality has been changed.  I just
   did this because it makes the code a lot simpler.
 - Simplified the code for the kernel_matrix() function.  I also made it a little more
   general.  So it should now support just about any possible combination of arguments
   that makes any kind of sense for creating a kernel matrix.

--HG--
extra : convert_revision : svn%3Afdd8eb12-d10e-0410-9acb-85c331704f74/trunk%403705