Make the concat list explicit

Since I decided to preen mocha and chai, we can no longer generate the
concat file list from the preen config. We must instead explicitly list
the modules we want to concatenate. I placed this config in bower.json
so that most of the time, we won't need to change the Gruntfile.

Also added a concatenation task for test page dependencies.

test/_test.js

@@ -0,0 +1,2 @@
+mocha.setup("bdd");
+window.assert = chai.assert;