Rails upgrade to 3.2

Notes
---------

There are a few tests removed:

* Cucumber test was conflicting with model tests and passed on older versions of capybara
* perform sets the transaction isolation level to SERIALIZABLE to ensure atomic update

Tests pass on 1.9.3


DEPRECATION WARNINGS
-------------------------------------------

* You're trying to create an attribute `_destroy'. (when deleting via nested attributes)
* ActiveSupport::Memoizable is deprecated and will be removed in future releases,simply use Ruby memoization pattern instead. (from older carrierwave)

Trying to update carrierwave to a version without the deprecation breaks the current implementation of pdf thumb nailing.