Added basic tests of unique and duplicated for integer64 columns

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1245 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added Rick's test distinguishing 1e-30 from 0.0 as from v1.9.2

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1246 edb9625f-4e0d-4859-8d74-9fd3b1da38cb