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/_pyio.py

@@ -19,33 +19,7 @@ else:
     _setmode = None
 
 import io
-from io import (SEEK_SET, SEEK_CUR, SEEK_END)
-
-__all__ = [
-    'BlockingIOError',
-    'BufferedIOBase',
-    'BufferedRWPair',
-    'BufferedRandom',
-    'BufferedReader',
-    'BufferedWriter',
-    'BytesIO',
-    'DEFAULT_BUFFER_SIZE',
-    'FileIO',
-    'IOBase',
-    'IncrementalNewlineDecoder',
-    'OpenWrapper',
-    'RawIOBase',
-    'SEEK_CUR',
-    'SEEK_END',
-    'SEEK_SET',
-    'StringIO',
-    'TextIOBase',
-    'TextIOWrapper',
-    'UnsupportedOperation',
-    '_io',
-    'abc',
-    'open',
-]
+from io import (__all__, SEEK_SET, SEEK_CUR, SEEK_END)
 
 valid_seek_flags = {0, 1, 2}  # Hardwired values
 if hasattr(os, 'SEEK_HOLE') :