move slash_join to prevent local imports

util/__init__.py

@@ -1,3 +1,18 @@
 def get_app_url(config):
   """ Returns the application's URL, based on the given config. """
   return '%s://%s' % (config['PREFERRED_URL_SCHEME'], config['SERVER_HOSTNAME'])
+
+
+def slash_join(*args):
+  """
+  Joins together strings and guarantees there is only one '/' in between the
+  each string joined. Double slashes ('//') are assumed to be intentional and
+  are not deduplicated.
+  """
+  def rmslash(path):
+    path = path[1:] if path[0] == '/' else path
+    path = path[:-1] if path[-1] == '/' else path
+    return path
+
+  args = [rmslash(path) for path in args]
+  return '/'.join(args)