Correct validators spec

This is part of the effort started at
https://github.com/thoughtbot/paperclip/issues/2199 to ensure the test
suite is green locally.

The validators spec was failing since the setup required was missing a
call to 'rebuild_class' and leaving the Dummy class in a bad state.

This PR adds the call to the before block setup.

This is part of the effort started at https://github.com/thoughtbot/paperclip/issues/2199)
to ensure the test suite is green locally.

This spec was failing on obtaining a S3 instance with an `nil` region
key. Since `Aws::Resource` does a regex match against the region key
passed in, we would fail on `NoMethodError`.

This corrects the issue by setting a region key to an empty string in
the test setup.

[fixes #1932]

Capistrano won't symlink the `public/system` folder by default anymore.
Capistrano needs to be configured accordingly.

See related issues:

* https://github.com/capistrano/capistrano/commit/033bf8ee492936787cd0744e69b3df8a5ad5b6e6#diff-348edd3e734eaeed0fe97af037f3c647
* https://github.com/capistrano/rails/issues/104
* https://github.com/capistrano/rails#symlinks

[fixes #2141]
[fixes #2166]

Clarify semantics of the only_process option (documentation-only)

This was really confusing to me, and I think this small change would help to clarify what's going on without having to trace through the code.

README elucidation for Ruby beginners

change 'show view' to 'view helpers'

Clarifying contributions.

Update README.md

Fixes #2130.

Added FactoryGirl configuration details

Fix outdated method description in helper module

Fixes #2130.

link in Readme to source code of Paperclip::Processor

for better visibility and better User experience of documentation

Most contributors don't know to update the NEWS file when submitting
code.

Currently paperclip fails with `NoMethodError` on `nil` when file is not
present. Since `nil` is proper response from fog on missing files, and
this method already returns `false` if any error happen (see line 178),
returning `false` here would be properly handled on client code.

[closes #2173]

Update NEWS.

[ci skip]

Adds failing spec to command line dup check

[fixes #1670]
[fixes #2169]

[fixes #2164]

Bugfix: Dynamic fog directory

`Paperclip::Storage::Fog#host_name_for_directory` assumes a String-like
object is set and doesn't check if `@options[:fog_directory]` is
callable, while `Paperclip::Storage::Fog#directory` does. This extracts
a new method with the condition and refactors the other two methods to
call it.

Fixes #2018, #2093.

@melissawahnish noticed that while we are on beta v5 will not be found.

[ci skip]

This configuration constant was useful for supporting different versions
of AWS SDK. We don't any longer, and we can set the value directly.

[fixes #2148]

* `AWS::Core` is an AWS SDK v1 API, we can drop it
* We don't use the "I attach a" cucumber step

Brings back warning on not supported SDK versions.

Related: https://github.com/thoughtbot/paperclip/commit/25be0b25d67923e28419c6146e8f8307741a974b#commitcomment-16831800

We don't support AWS SDK v1 any longer.

Drops Rails 3 branches.

[fixes #2101]

Update example to add mime-types to file extensions

Remove Rails 3 snippets

Rails 3 is not supported anymore. We can safely remove mentions and
snippets for it.

Drop unused variable definition (`options`).

The old example gives deprecation warnings from recent 2.x versions of mime-types. As of f0bd25ad the Gemfile also allows version 3.0 or newer. The new example should work regardless of the version of the mime-types gem. [skip ci]

`>= 2.0.34` is the proper restriction. We weren't allowing `2.0.33`
before.

Paperclip 5 no longer supports aws-sdk v1. Having a lot of constraints
in one gem dependency caused issues when pushing the gem (ref:
https://github.com/rubygems/rubygems/issues/1564).

This commit simplifies the dependency restriction to `>= 2.0.33`.

Pairing with @kitop