Issue 17755: test_builtin assumes LANG=C

I'm not sure about this one ... but it fails with an utf8 locale which happended to be set as the default, run from the installed location.

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FAIL: test_input_tty_non_ascii (test.test_builtin.BuiltinTest)
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Traceback (most recent call last):
  File "/home/tmp/lib/python3.4/test/test_builtin.py", line 1176, in test_input_tty_non_ascii
    self.check_input_tty("prompt\xe9", b"quux\xe9", "utf-8")
  File "/home/tmp/lib/python3.4/test/test_builtin.py", line 1167, in check_input_tty
    self.assertEqual(input_result, expected)
AssertionError: 'quux' != 'quux\udce9'
- quux
+ quux\udce9
?     +


======================================================================
FAIL: test_input_tty_non_ascii_unicode_errors (test.test_builtin.BuiltinTest)
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Traceback (most recent call last):
  File "/home/tmp/lib/python3.4/test/test_builtin.py", line 1180, in test_input_tty_non_ascii_unicode_errors
    self.check_input_tty("prompt\xe9", b"quux\xe9", "ascii")
  File "/home/tmp/lib/python3.4/test/test_builtin.py", line 1167, in check_input_tty
    self.assertEqual(input_result, expected)
AssertionError: 'quux' != 'quux\udce9'
- quux
+ quux\udce9
?     +