use Rack::Utils.unescape_path to unescape path_info

Unescaping paths is different from unescaping query parameters.  This
commit changes the unescape to use the URI parser to unescape the path,
which leaves `+` as `+`.

Fixes #265
References rails/rails#11816

HISTORY.md

@@ -1,3 +1,9 @@
+Fri Sep  4 14:15:32 2015  Aaron Patterson <tenderlove@ruby-lang.org>
+
+	* Files and directories with + in the name are served correctly.
+	Rather than unescaping paths like a form, we unescape with a URI
+	parser using `Rack::Utils.unescape_path`. Fixes #265
+
 Thu Aug 27 15:43:48 2015  Aaron Patterson <tenderlove@ruby-lang.org>
 
 	* Tempfiles are automatically closed in the case that there were too

lib/rack/file.rb

@@ -30,7 +30,7 @@ def call(env)
         return fail(405, "Method Not Allowed", {'Allow' => ALLOW_HEADER})
       end
 
-      path_info = Utils.unescape request.path_info
+      path_info = Utils.unescape_path request.path_info
       clean_path_info = Utils.clean_path_info(path_info)
 
       path = ::File.join(@root, clean_path_info)

test/spec_file.rb

@@ -10,6 +10,21 @@ def file(*args)
     Rack::Lint.new Rack::File.new(*args)
   end
 
+  it 'serves files with + in the file name' do
+    Dir.mktmpdir do |dir|
+      File.write File.join(dir, "you+me.txt"), "hello world"
+      app = file(dir)
+      env = Rack::MockRequest.env_for("/you+me.txt")
+      status,_,body = app.call env
+
+      assert_equal 200, status
+
+      str = ''
+      body.each { |x| str << x }
+      assert_match "hello world", str
+    end
+  end
+
   it "serve files" do
     res = Rack::MockRequest.new(file(DOCROOT)).get("/cgi/test")