Adding in special case to ignore.

Added in a special case to ignore the ns form.  At some point something more elegant could be done instead, but for now this fixes the problem.  The test only makes a difference on Clojure 1.5, but I've put the test in anyway as presumably the code will be migrated to 1.5 at some point.

Fixes https://github.com/lshift/cloverage/issues/48