Fix up bad simplifications; add tests of derivatives and simplifications.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/optimizer@869 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Add verbose argument to Deriv and Simplify and related functions.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/optimizer@870 edb9625f-4e0d-4859-8d74-9fd3b1da38cb