1. Added some instrumentation prints to trace code generation; I have a
better idea of how it works now.
2. DenseMatrixOpsExp.scala:
    a. Changed how the codegen is engaged. For some
reason, adding a println statement (staged as a Misc1_Println node) is
creating a dependency to a previous file reading node. This seems to be
a bigger issue - side stepping it by not using prints in the
matmult_impl function for now.
    a. Avoiding allocation of a new DenseMatrix when autotuning is
    enabled. This must be part of the driver function which calls the
    autotuned kernel. For now, the first matrix is both read from and written to, which is
    clearly wrong. Will fix in the next check in.
    b. Raw code for matrix multiply emitted into "kernelcode.cpp". It's
    just a blob of code - no header, no nothin'. More cleanups on the
    way.