Simplified ii to x in onLoad

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1067 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
+ Updated onLoad comments and FAQ 2.23 (for loop rather than one line)
+ Updated 3 vignettes on homepage

git-svn-id: svn+ssh://svn.r-forge.r-project.org/svnroot/datatable@1068 edb9625f-4e0d-4859-8d74-9fd3b1da38cb
Merge branch 'refs/heads/r-forge-git-svn-local'