Corrected timing for dcast.data.table in NEWS

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1169 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Edited NEWS.

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1170 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added gmean

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1171 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Merge branch 'refs/heads/r-forge-git-svn-local'
Fixes #5379 - dcast with factor cols on LHS along with drop=FALSE