- Also bump Travis Ruby 2.2.x version to 2.2.4

-   Also modify the appraisals to be more flexibly specified.
-   The specs are '>= 1.16' and '< 4.0' because the major versions of
    mime-types have steadily restricted the supported versions of Ruby at a
    different rate than Rails. The Appraisal for Rails 5 can be specified as
    either '>= 2.0, '< 4.0' or '~> 3.0' depending on how other gems restrict
    mime-types versions.

    -   mime-types 1.x supports any version of Ruby, but no longer receives any
        updates (it hit EOL on 27 October 2015).
    -   mime-types 2.x supports Ruby >= 1.9.2, but will only receive security
        and data updates until 21 November 2017.
    -   mime-types 3.x supports Ruby >= 2.0 and is the active development
        version of mime-types.

-   The APIs that paperclip uses are compatible between all three versions of
    mime-types.

TODO: Simpify lib/paperclip/storage/s3.rb

See:

* https://github.com/thoughtbot/paperclip/issues/2049

In preparation for Rails 5, which, when it is released, will make Rails
3.2 and 4.1 unsupported.

See:

* http://weblog.rubyonrails.org/2015/12/18/Rails-5-0-beta1/
* https://github.com/thoughtbot/paperclip/issues/2049

* update aruba methods for in_current_dir and check_file_presence
* switch rspec syntax from should to expect
* configure raise_in_transactional_callbacks if AR >= 4.2
* remove paperclip itself from Appraisal
This also updates Travis to use the default bundler (to enable caching) and to build primary rubies first

Change it from 3.2.15 to 3.2.0. We'll let bundler handle installing the
latest version. With `~>` the last number doesn't really matter anyway.

For the full details of what is included in this release, check out NEWS.

[fixes #1875]

This is a big one.

This change converts all of the existing tests from test/unit to RSpec.
It's been a long time coming, and was specifically prompted by the
inability of minitest to work with Appraisal across the various Rails
versions. Instead of ironing out that headache, converting to RSpec was
preferable (after initial probing).

Many assertions are still assertions and are housed in the Assertions
module, but they should be converted as they get touched. Similarly,
since we're touching all the tests/specs, we convert all the hashes from
1.8 syntax to 1.9 syntax.

This test will generate a basic Rails application, include Paperclip
into Gemfile, and call basic `has_attached_file` in the model. This will
make sure that we're not messing up any of the configuration and
integration for our gem and the Rails framework.

Update Gemfile to make sure we can run the test locally, and also upgrade Rails 3.1 beta to latest version

This will fix the problem with Psych on the old version of Rails 2.x