add SEEK_ constants to _pyio
diff --git a/Lib/_pyio.py b/Lib/_pyio.py
index 334c2b7..66cdc20 100644
--- a/Lib/_pyio.py
+++ b/Lib/_pyio.py
@@ -14,6 +14,7 @@
 
 import io
 from io import __all__
+from io import SEEK_SET, SEEK_CUR, SEEK_END
 
 # open() uses st_blksize whenever we can
 DEFAULT_BUFFER_SIZE = 8 * 1024  # bytes