Added dsorted and csorted to forder.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1126 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added 2 tests that forder doesn't pass yet.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1127 edb9625f-4e0d-4859-8d74-9fd3b1da38cb