Creorder now ignores the beginning and end of ordering vectors where that region doesn't change the row ordering,  such as c(1:500, 502, 501, 503:nrow).   Creorder(DT, 1:nrow) will now return instantly.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1082 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Improved error checks in Creorder

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1083 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added check to Creorder that  start <= o[start:end] <= end, just to be safe and robust.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1084 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Changed Creorder to accept plain vectors too. Hence Csetreordervec removed so that the new checks on o and start:end efficiency are central in a single function.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1085 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
minor fixes to `setDT`

    `setDT` lost ExtPtr ref. is now fixed.
    Class attributes to data.frame are now preserved.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1086 edb9625f-4e0d-4859-8d74-9fd3b1da38cb