as the former is deprecated and throws a warning.

File.exists? has been deprecated since Ruby 1.9.2

Fixes #1520

This should make it possible to avoid passing a :geometry in the style
definition (when passing it as a hash), thus making Paperclip avoid resizing the
image. This is helpful when you want to perform your own custom
resizing/cropping using :convert_options rather than the default options offered
by Paperclip itself.

Fixes #1550

* Extract private methods
* Remove trailing conditionals
* Remove explicit returns
* Remove `.self`

There's nothing they can be spoofing, and there's little danger of a
webserver accidentally sending a dangerous Content-Type with a file that
has no extension. If the browser chooses to interpret it in a dangerous
manner, no server-side library on earth can change that.

This isn't specifically related to RSpec, but is built off the branch
and is part of an effort to get the CI build green.

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.

The `file` command on OS X takes the --mime-type option, which returns
only the type and not the optional encoding. This is nice, but it's not
portable. Use --mime and strip the encoding off if it's there.

And don't forget this time.

Validators love instances. Seriously, though, this was causing a problem
when the validator was being called and the private "send" didn't have
an instance to work on.

It resulted with downloading attachment (i.e. from S3) on each
instance validation even when attachment didn't change at all.