CLC-3633 Copy hashed precompiled assets to their unhashed names, for ben...

...efit of load tests

https://jira.ets.berkeley.edu/jira/browse/CLC-3633

Rails 4 asset compilation no longer leaves the files available via their unhashed name. Fix is to copy the hashed file over to their unhashed equivalent after compilation, as described on this blog post: http://dev.mensfeld.pl/2013/07/upgrading-to-rails-4-0-from-rails-3-2-test-case-part-ii-assets-models/

The rake task is also shamelessly stolen from that page.