Check if connected before applying automatic validations.

Real world need this solves:

* I needed to pre-compile my assets for production in an environment without
  access to the production database server.
* I enable "config.assets.initialize_on_precompile" in my application.rb
  to allow for this. Now assets will compile without initializing rails.
* Since I am running in production mode config.eager_load is enabled
  in my environments/production.rb file.

Without this patch the eager loading loads my models which calls
enforce_schema_rules which starts a database connection so it can scan
the table for validations.

With this patch enforce_schema_rules will only do it's scan if we already
have a database connection. In a normal web or console environment we will
have a connection since Rails will initialize.
Update Rakefile to use Bundler and update tests

The Rakefile was using some custom tasks to handle packaging and release.
This will make it use Bundler meaning less code and more specified
dependencies.

Also updated the dependencies and tests so the test suite will run under
the latest Rails and Ruby.