Namespaces being tested multiple times

[crisptrutski]

When inferring namespaces from the fileset, certain namespaces may be included multiple times, due to various files appearing in multiple commits, eg. via transformation. No amount of redundant sources seem to justify extra execution and reporting though 😄

In the particular case I've seen, which is running boot-test directly after boot-cljs-test, I'm not actually even transforming these particular files - I'm just adding a new file (a "suite" namespace to run the tests) Interestingly this causes .cljc tests to run twice, but not the .clj ones.

Please see this branch if you'd like to reproduce, particularly if you think that I've made a mistake in my use of the fileset API.