config: pass some optional args as keywords

This makes it a little more obvious that self.read is being passed as
include, which took me a moment to figure out.

mercurial/config.py

@@ -170,4 +170,5 b' class config(object):'
     def read(self, path, fp=None, sections=None, remap=None):
         if not fp:
             fp = util.posixfile(path, 'rb')
-        self.parse(path, fp.read(), sections, remap, self.read)
+        self.parse(path, fp.read(),
+                   sections=sections, remap=remap, include=self.read)