Update Rakefile to my latest template version

* Add a 'clean' task
* Fix an issue when there are no repository fixtures

Rakefile

@@ -43,6 +43,7 @@ task :spec_prep do
     File::exists?(target) || system("git clone #{repo} #{target}")
   end
 
+  FileUtils::mkdir_p("spec/fixtures/modules")
   fixtures("symlinks").each do |source, target|
     File::exists?(target) || FileUtils::ln_s(source, target)
   end
@@ -77,6 +78,11 @@ task :build do
   end
 end
 
+desc "Clean a built module package"
+task :clean do
+  FileUtils.rm_rf("pkg/")
+end
+
 desc "Check puppet manifests with puppet-lint"
 task :lint do
   # This requires pull request: https://github.com/rodjek/puppet-lint/pull/81