A possible fix for #1036

I can only assume that the only possible thing to close on a session are the
adapters. As such, I wrote the close method for a session object which closes
all possible adapters.

requests/sessions.py

@@ -365,7 +365,12 @@ class Session(SessionRedirectMixin):
                 return adapter
 
         # Nothing matches :-/
-        raise InvalidSchema('No connection adapters were found for \'%s\'' % url)
+        raise InvalidSchema("No connection adapters were found for '%s'" % url)
+
+    def close(self):
+        """Closes all adapters and as such the session"""
+        for _, v in self.adapters.items():
+            v.close()
 
     def mount(self, prefix, adapter):
         """Registers a connection adapter to a prefix."""