Move previous runtime dependencies to development dependencies.

test/test_coffeescript.rb

@@ -3,6 +3,7 @@ require 'helper'
 class TestCoffeeScript < Test::Unit::TestCase
   context "converting CoffeeScript" do
     setup do
+      External.require_with_graceful_fail('jekyll-coffeescript')
       @site = fixture_site
       @site.process
       @test_coffeescript_file = dest_dir("js/coffeescript.js")

test/test_configuration.rb

@@ -181,6 +181,8 @@ class TestConfiguration < Test::Unit::TestCase
     end
 
     should "load multiple config files" do
+      External.require_with_graceful_fail('toml')
+
       mock(SafeYAML).load_file(@paths[:default]) { Hash.new }
       mock(SafeYAML).load_file(@paths[:other]) { Hash.new }
       mock(TOML).load_file(@paths[:toml]) { Hash.new }