Merge pull request RustPython#1514 from alanjds/fix-1132-sys-stdout

`sys.std{in,out,err}` implemented in the most simple way

Author: windelbouwman

Lib/_sitebuiltins.py

@@ -8,8 +8,14 @@
 # Note this means this module should also avoid keep things alive in its
 # globals.
 
+import os
 import sys
 
+sys.stdin = sys.__stdin__ = getattr(sys, '__stdin__', False) or os.fdopen(0, "r")
+sys.stdout = sys.__stdout__ = getattr(sys, '__stdout__', False) or os.fdopen(1, "w")
+sys.stderr = sys.__stderr__ = getattr(sys, '__stderr__', False) or os.fdopen(2, "w")
+
+
 class Quitter(object):
     def __init__(self, name, eof):
         self.name = name