Begin incorporating Python unit tests into build

We now build a separate APE binary for each test so they can run in
parallel. We've got 148 tests running fast and stable so far.

third_party/python/Lib/test/test_codeccallbacks.py

@@ -4,6 +4,7 @@ import sys
 import test.support
 import unicodedata
 import unittest
+from encodings import raw_unicode_escape
 
 class PosReturn:
     # this can be used for configurable callbacks