fixing R-forge Matrix bug #5933 (matrix-matrix prod with 0-extents)
R-(3.2.0) compatible behavior of matrix products (%*%, [t]crossprod), now at least for
sparseVectors

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/matrix@3010 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
misc. matrix-product related cleanups

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/matrix@3011 edb9625f-4e0d-4859-8d74-9fd3b1da38cb