Change RuntimeError into IOError when module file not found on reload.
diff --git a/Python/import.c b/Python/import.c
index c654940..7725245 100644
--- a/Python/import.c
+++ b/Python/import.c
@@ -152,7 +152,7 @@
 		if (m == NULL)
 			err_setstr(NameError, name);
 		else
-			err_setstr(RuntimeError, "no module source file");
+			err_setstr(IOError, "no module source file");
 		return NULL;
 	}
 	/* Get mtime -- always useful */