Standardize on `expect` syntax.
Avoid deprecation warning.
Stop monkey patching the matcher class.

The monkey patching code originated in rspec-rails
when it was a separate code base from the matcher
definition in rspec-expectations, but now that they
live in the same code base, it's best not to
monkey patch.

Also, we don't need to limit this to just when rails
is loaded; nothing in the logic relies on rails. We
were only relying on rails for `alias_method_chain` and
`ActiveSupport::Concern`.
Pull in `errors_on` active model extension from rspec-rails.
Update gem file to install the right versions of rails gems.
Merge pull request #15 from rspec/import-rspec-rails-extensions

Import rspec rails extensions