Added fully reversed test to bench().  isorted now returns -1 only when strictly decreasing, otherwise rev() would be unstable for ties.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1089 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added baseline switch to bench() for dev test

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1090 edb9625f-4e0d-4859-8d74-9fd3b1da38cb