share extractor and downloader sessions

There was never any "good" reason for the strict separation
between extractors and downloaders. This change allows for
reduced resource usage (probably unnoticeable) and less lines
of code at the "cost" of tighter coupling.

gallery_dl/job.py

@@ -79,12 +79,6 @@ class Job():
             if self.pred_queue:
                 self.handle_queue(msg[1])
 
-        elif msg[0] == Message.Headers:
-            self.handle_headers(msg[1])
-
-        elif msg[0] == Message.Cookies:
-            self.handle_cookies(msg[1])
-
         elif msg[0] == Message.Version:
             if msg[1] != 1:
                 raise "unsupported message-version ({}, {})".format(
@@ -101,12 +95,6 @@ class Job():
     def handle_queue(self, url):
         """Handle Message.Queue"""
 
-    def handle_headers(self, headers):
-        """Handle Message.Headers"""
-
-    def handle_cookies(self, cookies):
-        """Handle Message.Cookies"""
-
     def update_kwdict(self, kwdict):
         """Add 'category' and 'subcategory' keywords"""
         kwdict["category"] = self.extractor.category
@@ -145,12 +133,6 @@ class DownloadJob(Job):
         except exception.NoExtractorError:
             self._write_unsupported(url)
 
-    def handle_headers(self, headers):
-        self.get_downloader("http:").set_headers(headers)
-
-    def handle_cookies(self, cookies):
-        self.get_downloader("http:").set_cookies(cookies)
-
     def get_downloader(self, url):
         """Return, and possibly construct, a downloader suitable for 'url'"""
         pos = url.find(":")
@@ -160,7 +142,7 @@ class DownloadJob(Job):
         instance = self.downloaders.get(scheme)
         if instance is None:
             klass = downloader.find(scheme)
-            instance = klass(self.out)
+            instance = klass(self.extractor.session, self.out)
             self.downloaders[scheme] = instance
         return instance
 
@@ -300,13 +282,10 @@ class DataJob(Job):
         # collect data
         try:
             for msg in self.extractor:
-                if msg[0] in (Message.Headers, Message.Cookies):
-                    copy = (msg[0], dict(msg[1]))
-                else:
-                    copy = [
-                        part.copy() if hasattr(part, "copy") else part
-                        for part in msg
-                    ]
+                copy = [
+                    part.copy() if hasattr(part, "copy") else part
+                    for part in msg
+                ]
                 self.data.append(copy)
         except Exception as exc:
             self.data.append((exc.__class__.__name__, str(exc)))