Refactor all the diff code into a single dir

setup/extensions.py

@@ -90,7 +90,7 @@ extensions = [
         ),
 
     Extension('_patiencediff_c',
-        ['calibre/utils/diff/_patiencediff_c.c'],
+        ['calibre/gui2/tweak_book/diff/_patiencediff_c.c'],
         ),
 
     Extension('icu',

src/calibre/gui2/tweak_book/diff/main.py

@@ -0,0 +1,10 @@
+#!/usr/bin/env python
+# vim:fileencoding=utf-8
+from __future__ import (unicode_literals, division, absolute_import,
+                        print_function)
+
+__license__ = 'GPL v3'
+__copyright__ = '2014, Kovid Goyal <kovid at kovidgoyal.net>'
+
+
+