doctest should normalize tabs when comparing output

Lib/test/test_doctest.py

 # -*- coding: utf-8 -*-
 """
 Test script for doctest.
 """
 
 import sys
 from test import test_support
 import doctest
 
 # NOTE: There are some additional tests relating to interaction with
@@ skipping 2047 matching lines @@
 def test_trailing_space_in_test():
     """
     Trailing spaces in expected output are significant:
 
       >>> x, y = 'foo', ''
       >>> print x, y
       foo \n
     """
 
 def test_tabs_in_test():
-    """
+    r"""
     Tabs are expanded correctly:
 
       >>> print "\tx"
         x
     """
 
 def test_unittest_reportflags():
     """Default unittest reporting flags can be set to control reporting
 
     Here, we'll set the REPORT_ONLY_FIRST_FAILURE option so we see
@@ skipping 404 matching lines @@
     r = tracer.results()
     print 'Writing coverage results...'
     r.write_results(show_missing=True, summary=True,
                     coverdir=coverdir)
 
 if __name__ == '__main__':
     if '-c' in sys.argv:
         test_coverage('/tmp/doctest.cover')
     else:
         test_main()