Use atomic file rename instead of move

updated patch for commit in #1545164: Full absolute url is returned to core JS aggregation, requiring HTTP request to aggregate file contents

committed

oops, Alan points out in the case where we are re-aggregating we need $success to default to TRUE.

moves tests to a sub-directory, fixes the test in terms of admin theme permission added in and adds a test that should

re: admin theme see: #1423370: JavaScript libraries aren't loaded on some 403 pages or on "admin" pages that really aren't for admins

committed that, but I'm concerned the condition is still not correct.

Here's a test that show it failing.

reposting for testbot

Here's with another fix that satisfies the added test case in #10.

committed