Fix `Cell.rails3_1_or_more?`, `Cell.rails3_2_or_more?` and
`Cell.rails4_0_or_more?` methods
Merge pull request #179 from kuraga/patch-2

Fix `Cell.rails3_1_or_more?`, `Cell.rails3_2_or_more?` and `Cell.rails4_0_or_more?` methods
use rails 3.0.20 and fix a test bug where a config flag (relative_url_root) wasn't set.
make all tests run for 4.0.0.
don't test encoding in 3.2 and jruby.