Fixed #5376. := adds new cols on empty data.tables as well.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1228 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Wrapping up 'order' and 'setorder'

+ All instances of 'forder' renamed to 'forderv': naming consistency
+ 'fast_order' renamed to 'forder' : naming consistency
+ 'DT[order(x, -y, …)]' automatically optimised to 'DT[forder(DT, x, -y, …)]'.
+ Test added for above change.
+ Updated news with entry for '?setorder' and 'DT[order(…)]' optimisation

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1229 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Fixing the mess (learning to rollback using git). Ignore commits from #1228 until here. Reverting to #1227 basically.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1230 edb9625f-4e0d-4859-8d74-9fd3b1da38cb