Handle ImproperlyConfigured when trying to load the S3 backend.

If django-storages is installed, but boto is not, it will raise an
ImproperlyConfigured exception when trying to do the import, which we didn't
catch. This caused the admin form to error out.

Testing done:
Removed the boto package from my site-packages and tried to load the file
storage settings page. When I selected "Amazon S3", saw the error message from
the exception.

Fixes bug 3062.

Reviewed at https://reviews.reviewboard.org/r/4463/
Fix alignment of the file attachment thumbnail overlay.

We put a clickable overlay on top of file attachment thumbnails, to ensure that
clicking anywhere within the area of the attachment will redirect to the review
UI (instead of selecting text or accidentally activating any links that might
be part of the thumbnail, e.g. for text file types). This overlay wasn't set to
have a left alignment of 0, so its left edge was aligned with the thumbnail
itself. This worked for some types (like text) but failed when we had
thumbnails that didn't stretch the full width of the box.

Testing done:
Verified alignment in Chrome and Firefox.

Reviewed at https://reviews.reviewboard.org/r/4475/
Add built locale files to .gitignore in release-1.7.x

We don't have any locale files in release-1.7.x, but the built .mo files may be
left over from when people were using master. Ignore them here, too.
Split RB.linkifyText into separate pieces.

The linkifyText method does a bunch of things. It starts out by escaping out <
and > characters (which doesn't have much to do with linkifying), and then
proceeds to create links for any full URLs, /r/### review requests, and bug
numbers.

When we integrate markdown support for text boxes, we don't want the <>
escaping, and full URLs will be handled by the markdown parser. We therefore
want to be able to call subsets of this functionality in addition to the whole.

Testing done: Ran js-tests
Reviewed at https://reviews.reviewboard.org/r/4489/
Make field formatters in ReviewRequestEditorView set the element's html.

ReviewRequestEditorView's field definitions have an abstract "formatter"
concept, which was a function that would mutate the value before setting it in
the DOM. This change moves the responsibility for calling jQuery.html() into
the formatter functions themselves. The motivation for this is that the coming
markdown changes will need to do some fancier stuff including accessing data
attributes on the element (to check if it should be formatted as rich text),
and setting the rich-text class once it's been formatted.

Testing done: Ran js-tests.
Reviewed at https://reviews.reviewboard.org/r/4490/
Fix up more PEP-8 issues.

This handles scmtools, site, ssh, and webapi subdirs, as well as the top-level
scripts.

Testing done: Ran unit tests
Reviewed at https://reviews.reviewboard.org/r/4473/
Rename scmtools.crypto to scmtools.crypto_utils

On case-insensitive file systems, the import of 'Crypto' inside
scmtools.crypto will fail. This problem also appears when attempting to
run Review Board inside a Linux Virtual Machine, where the code has been
shared from a Mac OSX Host. Since the default OSX filesystem is
case-insensitive, case-preserving, the import will fail as well.

Reviewed at https://reviews.reviewboard.org/r/4483/
Merge branch 'release-1.7.x'