Effectively renamed tokenize_tests.py to have a txt extension instead.

This file isn't meant to be executed, it's data input for test_tokenize.py.
The problem with the .py extension is that it uses "non-standard"
indentation, and it's good to test that, but reindent.py keeps wanting
to fix it.  But fixing the indentation causes the expected-output file to
change, since exact line and column numbers are part of the
tokenize.tokenize() output getting tested.

Lib/test/test_tokenize.py

@@ -4,7 +4,7 @@ import tokenize, os, sys
 if verbose:
     print 'starting...'
 
-f = file(findfile('tokenize_tests'+os.extsep+'py'))
+f = file(findfile('tokenize_tests' + os.extsep + 'txt'))
 tokenize.tokenize(f.readline)
 f.close()