Fix Image.download method

- The method has been broken since the move to requests (wrong number of args sent to self.site.connection.get)
- Add option to stream the file to a file object

mwclient/image.py

@@ -25,13 +25,27 @@ def imageusage(self, namespace=None, filterredir='all', redirect=False,
     def duplicatefiles(self, limit=None):
         return mwclient.listing.PageProperty(self, 'duplicatefiles', 'df', dflimit=limit)
 
-    def download(self):
+    def download(self, destination=None):
+        """
+        Download the file. If `destination` is given, the file will be written
+        directly to the stream. Otherwise the file content will be stored in memory
+        and returned (with the risk of running out of memory for large files).
+
+        Recommended usage:
+
+            >>> with open(filename, 'wb') as fd:
+            ...     image.download(fd)
+
+        Args:
+            destination (file object): Destination file
+        """
         url = self.imageinfo['url']
-        if not url.startswith('http://'):
-            url = 'http://' + self.site.host + url
-        url = urllib.parse.urlparse(url)
-        # TODO: query string
-        return self.site.connection.get(url[1], url[2])
+        if destination is not None:
+            res = self.site.connection.get(url, stream=True)
+            for chunk in res.iter_content(1024):
+                destination.write(chunk)
+        else:
+            return self.site.connection.get(url).content
 
     def __repr__(self):
         return "<Image object '%s' for %s>" % (self.name.encode('utf-8'), self.site)