Tried to make gem more robust to no flann_get_distance_type and

flann_get_distance_order functions.

src/ruby/lib/flann.rb

@@ -271,8 +271,11 @@ def cluster dataset, clusters, parameters = {}
   attach_function :flann_free_index_double, [:index_ptr, :index_params_ptr], :int
 
   attach_function :flann_set_distance_type, [:distance_type, :int], :void
-  attach_function :flann_get_distance_type, [], :distance_type
-  attach_function :flann_get_distance_order, [], :int
+  begin
+    attach_function :flann_get_distance_type, [], :distance_type
+    attach_function :flann_get_distance_order, [], :int
+  rescue FFI::NotFoundError
+  end
 
   attach_function :flann_compute_cluster_centers_byte,    [:pointer, :int, :int, :int, :pointer, :index_params_ptr], :int
   attach_function :flann_compute_cluster_centers_int,     [:pointer, :int, :int, :int, :pointer, :index_params_ptr], :int

src/ruby/spec/flann_spec.rb

@@ -68,10 +68,13 @@
 
   context "#set_distance_type!" do
     it "sets the distance functor without error" do
-      #pending "distance type unsupported in the C bindings, use the C++ bindings instead"
       Flann.set_distance_type! :euclidean
-      d = Flann.get_distance_type
-      expect(d).to eq(:euclidean)
+
+      # Version check needed before attempting get_distance_type
+      if Flann.respond_to?(:flann_get_distance_type)
+        d = Flann.get_distance_type
+        expect(d).to eq(:euclidean)
+      end
     end
   end