setup.py: make warning sound less intimidating

setup.py

@@ -209,12 +209,10 @@ class kwant_sdist(sdist):
         sdist.run(self)
 
         if names is None:
-            print(banner(' Warning '),
-
+            print(banner(' Caution '),
         """Git was not available to generate the list of files to be included in the
-source distribution.  The old MANIFEST.in was used.""",
-                  banner(),
-                  sep='\n', file=sys.stderr)
+source distribution.  The old {} was used.""".format(MANIFEST_IN_FILE),
+                  banner(), sep='\n', file=sys.stderr)
 
     def make_release_tree(self, base_dir, files):
         sdist.make_release_tree(self, base_dir, files)