Add test to prevent regression regarding excessive logging

Fix a nil error in failure_message of content type validation matcher

[ci skip]

When a matcher uses both `allowing` and `rejecting`, and validation fails,
`@missing_rejected_types` might still be `nil`.

When a matcher only uses either of the two, a part of the message is `nil`.

Note: this is most likely not the way we want to test our matchers, but it
demonstrates the current issue.

Excessive logging can fill up disk space and become a denial of service attack, see https://cwe.mitre.org/data/definitions/779.html

[fixes #2016]

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

The attachment processing spec was failing since the setup required done
in a before block, namely a call to `rebuild_class`, was running
restricted to one of two contexts in the test file.
This was leaving the `Dummy` class in a bad state and affected other tests.

This PR moves the `before` block to run for the both of the contexts.

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