Gone back (hopefully temporarily) to using collage load-image function

while I try to sort out the resources issue. This isn't very satisfactory,
as the collage distribution is compiled using Java 7, which is going to
break for some people, and because I'm bloating my code with two separate
image libraries.

test/mw_engine/heightmap_test.clj

@@ -1,11 +1,12 @@
 (ns mw-engine.heightmap-test
+  (:use clojure.java.io)
   (:require [clojure.test :refer :all]
             [mw-engine.heightmap :refer :all]
             [clojure.math.combinatorics :as combo]))
 
 (deftest apply-heightmap-test
   (testing "Heightmap functionality"
-           (let [world (apply-heightmap "heightmaps/test9x9.png")
+           (let [world (apply-heightmap (as-file "resources/heightmaps/test9x9.png"))
                  altitudes (map #(:altitude %) (flatten world))
                  gradients (map #(:gradient %) (flatten world))]
              (is (= (count world) 9) "World should be 9x9")