avoid auto proxy detection when no_proxy is set

lib/net/http/persistent.rb

@@ -616,6 +616,8 @@ def connection_for uri
     if @proxy_uri and not proxy_bypass? uri.host, uri.port then
       connection_id << @proxy_connection_id
       net_http_args.concat @proxy_args
+    elsif proxy_bypass? uri.host, uri.port then
+      net_http_args.concat [nil]
     end
 
     connection = connections[connection_id]

test/test_net_http_persistent.rb

@@ -928,6 +928,21 @@ def test_proxy_bypass_double_comma
     refute @http.proxy_bypass? 'example.org', 80
   end
 
+  def test_connection_for_no_proxy_from_env
+    ENV['http_proxy'] = 'proxy.example'
+    ENV['no_proxy'] = 'localhost, example.com,'
+    ENV['proxy_user'] = 'johndoe'
+    ENV['proxy_password'] = 'muffins'
+
+    http = Net::HTTP::Persistent.new nil, :ENV
+
+    c = http.connection_for @uri
+
+    assert c.started?
+    refute c.proxy?
+    refute c.proxy_from_env? unless RUBY_1
+  end
+
   def test_reconnect
     result = @http.reconnect