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.

For some reason the test in this PR would make all other ones blow up.
For reasons not fully understood at the time of writing, the alternate
spec I'd written doesn't. So, we'll replace that test with this one and
it'll be green.