Detect when . is part of the :source-paths

[vemv]

Context

I received a report of a pretty extreme edge case: a bad cljalias combination would result in a classpath with both . and src in it.

It is contradictory becase one is a subset of the other, so clojure namespaces won't have a well-defined place where they should reside.

This results in namespace-filename-mismatches, which are confusing for end users.

Task

If . and a dir that is a subset of . are both part of the classpath, fail fast and informatively.