Python: Make Client::HttpRequest extend ControlFlowNode

Taus poitned out that the reuqest being send off, doesn't *need* to happen on a
CallNode. Someone *could* use a __setattr__ or property :\

Author: RasmusWL

python/ql/src/semmle/python/web/Http.qll

@@ -121,7 +121,7 @@ module Client {
       * conn = HTTPConnection('example.com')
         conn.request('GET', '/path')
       */
-    abstract class HttpRequest extends CallNode {
+    abstract class HttpRequest extends ControlFlowNode {
 
         /** Get any ControlFlowNode that is used to construct the final URL.
           *

python/ql/src/semmle/python/web/client/Requests.qll

@@ -6,7 +6,7 @@
 import python
 private import semmle.python.web.Http
 
-class RequestsHttpRequest extends Client::HttpRequest {
+class RequestsHttpRequest extends Client::HttpRequest, CallNode {
     CallableValue func;
     string method;
 

python/ql/src/semmle/python/web/client/StdLib.qll

@@ -18,7 +18,7 @@ ClassValue httpConnectionClass() {
     result = Value::named("six.moves.http_client.HTTPSConnection")
 }
 
-class HttpConnectionHttpRequest extends Client::HttpRequest {
+class HttpConnectionHttpRequest extends Client::HttpRequest, CallNode {
     CallNode constructor_call;
     CallableValue func;