Allow Importer objects to be placed onto the load path using add_import_path.

Closes #392.

lib/compass/configuration/adapters.rb

@@ -13,8 +13,13 @@ module Compass
         Compass::Frameworks::ALL.each do |framework|
           locations << [framework.stylesheets_directory, File.join(css_path || css_dir || ".", framework.name)]
         end
+        load_paths = []
         resolve_additional_import_paths.each do |additional_path|
+          if additional_path.is_a?(String)
             locations << [additional_path, File.join(css_path || css_dir || ".", File.basename(additional_path))]
+          else
+            load_paths << additional_path
+          end
         end
         plugin_opts = {:template_location => locations}
         plugin_opts[:style] = output_style if output_style
@@ -23,13 +28,14 @@ module Compass
         plugin_opts[:cache_location] = cache_path unless cache_path.nil?
         plugin_opts.merge!(sass_options || {})
         plugin_opts[:load_paths] ||= []
+        plugin_opts[:load_paths] += load_paths
         plugin_opts[:load_paths] << Compass::SpriteImporter.new
         plugin_opts
       end
 
       def resolve_additional_import_paths
         (additional_import_paths || []).map do |path|
-          if project_path && !absolute_path?(path)
+          if path.is_a?(String) && project_path && !absolute_path?(path)
             File.join(project_path, path)
           else
             path

test/units/configuration_test.rb

@@ -240,6 +240,21 @@ EXPECTED
     assert_correct expected_serialization.split("\n"), Compass.configuration.serialize.split("\n")
   end
 
+  def test_additional_import_paths_can_be_importers
+    contents = StringIO.new(<<-CONFIG)
+      http_path = "/"
+      project_path = "/home/chris/my_compass_project"
+      css_dir = "css"
+      additional_import_paths = ["../foo"]
+      add_import_path Sass::Importers::Filesystem.new("/tmp/foo")
+    CONFIG
+
+    Compass.add_configuration(contents, "test_additional_import_paths")
+
+    assert Compass.configuration.sass_load_paths.find{|p| p.is_a?(Sass::Importers::Filesystem) && p.root == "/tmp/foo"}
+    assert Compass.configuration.to_sass_plugin_options[:load_paths].find{|p| p.is_a?(Sass::Importers::Filesystem) && p.root == "/tmp/foo"}
+  end
+
   def test_config_with_pathname
     contents = StringIO.new(<<-CONFIG)
       http_path = "/"