Use #rm_rf rather than #remove_entry_secure

On some systems, `FileUtils#remove_entry_secure` fails to work because
it fails the [TOCTTOU vulnerability check](1), even for `/tmp`. In the
case of nanoc, the vulnerability check has little use, since it deletes
the directories that it creates itself, so using `FileUtils#rm_rf`
instead of `FileUtils#remove_entry_secure` is fine.

Also see nanoc/nanoc#465

[1]: http://www.ruby-doc.org/stdlib-2.1.2/libdoc/fileutils/rdoc/FileUtils.html#method-c-remove_entry_secure
wrap data source use/unuse in transaction so we are sure of the unuse
Merge pull request #491 from mpapis/features/ensure_datasources_unuse

Wrap data source #use/#unuse in transaction
Fix support for dotfiles in data-sources

    .htaccess and .htpasswd were not handled by any data-source
Merge pull request #492 from andydrop/release-3.7.x

Fix support for dotfiles in data-sources
Merge pull request #474 from nanoc/rm-rf-instead-of-remove-entry-secure

Use #rm_rf rather than #remove_entry_secure
Update Gemfile.lock
Add release notes for 3.7.4
Revert "Fix support for dotfiles in data-sources"
Merge pull request #497 from nanoc/revert-492-release-3.7.x

Revert "Fix support for dotfiles in data-sources"
Remove #492 from release notes
Add #476 to release notes
Merge pull request #496 from nanoc/add-3.7.4-release-notes

Add release notes for 3.7.4
Set version to 3.7.4
Set release date to today
updated nanoc version in Gemfile.lock
remove Gemfile.lock
Merge pull request #499 from nanoc/bugfix/remove_Gemfile_lock

Remove Gemfile.lock
Fix many Rubocop offenses

This is the second part of my crusade against non-standard code style;
the first part being #476. There are two reasons why these changes were
not in #476:

1. Rubocop got updated with a lot of new checks, and this PR ensures we
   adhere to the guidelines set forth in that new Rubocop.

2. I got over the attachment to my personal preferences (such as TODO’s
   not being postfixed by a colon).
Merge pull request #500 from nanoc/more-style-fixes

More style fixes