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.

PCbuild/python20.wse

@@ -2357,6 +2357,12 @@ item: Install File
   Description=Python Test files
   Flags=0000000000000010
 end
+item: Install File
+  Source=..\lib\test\*.txt
+  Destination=%MAINDIR%\Lib\test
+  Description=Python Test files
+  Flags=0000000000000010
+end
 item: Remark
 end
 item: Install File