Fixed segfault Arun found with forder

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1132 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1133 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Added extra checks to savetl_init and savetl_end.  (As previous commit message should have said).

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1134 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
More size_t tidy up

git-svn-id: svn://svn.r-forge.r-project.org/svnroot/datatable@1135 edb9625f-4e0d-4859-8d74-9fd3b1da38cb