README updated (for Debian-based Linux distros)

Other Debian based distros add in Ubuntu installation line

Test against Ruby 2.2.3 on Travis.

Removes `column_type` and `column_options` so that it works well in both
versions.

[closes #1947]

This reverts commit f6f5ea1b.

[closes #1966]

[closes #1965]

[fixes #1967]

Turns out it didn't fix test failures like I thought. It only added
more!

This reverts commit b8221c6b.

Cucumber needs to tell FakeWeb the s3_domain_url path for uploading a file, and FakeWeb needs to return XML

Both v1 and v2 of the AWS Ruby SDK accept the string literal AES256, no need to differentiate. (thank you, @trevorrowe)

Further changes to Paperclip::Storage::S3 for choosing aws-sdk-v2 before aws-sdk-v1; use object.upload_file rather than object.put; implement v2 expiring_url method

Fix GeometryParser for '@>' special case

According to the ImageMagick documentation the '@' flag is a special case that
can be used in conjunction with '>' to prevent IM from scaling an image up.
The '<' flag is ignored when using '@'.

http://www.imagemagick.org/Usage/resize/#pixel

This fixes the issue I reported in #1851

Fix specs broken by aruba changes

* 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

[ci skip] Add Ubuntu install instructions

Update version in README

You guys missed the version update for the gemfile entry.

It should never be the case that `url` returns `nil`. If there is no url
that can be reasonable achieved, as is the case when the record the
attachment is attached to is unpersisted, then `url` should return the
default url.