Fix vector libspecs

[athos]

This PR makes it possible to use lists and vectors totally interchangeably to represent libspecs in the ns macro.

The current implementation handles libspecs represented with a list and ones represented with a vector in different ways. Especially, only list libspecs are allowed to have prefix lists. So, for example, it can deal with something like:

(ns example.foo
  (:require (example [bar :as bar]
                     [baz :as baz])))
          ; ^ a list libspec

but not:

(ns example.foo
  (:require [example [bar :as bar]
                     [baz :as baz]]))
          ; ^ a vector libspec

A lot of Clojure libraries out there are using lists and vectors interchangeably in their ns declarations. It would make more people (including me) happy if ns-tracker could deal with forms like that :)

[athos]

Sorry, I wasn't aware some tests failed, but just fixed.

[weavejester]

Can you write some tests for this?

[athos]

Just added tests (along with it, I fixed a bug found on the way).

[weavejester]

Can you squash your commits down, and ensure that the commit summary line is under 70 characters?

[athos]

Done.