SDenv$.BY allocation moved down from R into C since 1-row subsets using `logicalVector[1]` now return R_TrueValue. Thanks to Luke for hardware watchpoint and guidance.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1177 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
write.table test back on without copy(DT) workaround. Fixed by the previous fix for write-to-R_TrueValue since Rdevel change on 11 Feb.

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1178 edb9625f-4e0d-4859-8d74-9fd3b1da38cb