After creating experimental patch, I could supress dialog
and error message on VS8.0. But it seems there is no way to
suppress error message on VC6. That is,

FAILED (failures=1)
Traceback (most recent call last):
  File "e:\python-dev\py3k\lib\runpy.py", line 160, in _run_module_as_main
    "__main__", fname, loader, pkg_name)
  File "e:\python-dev\py3k\lib\runpy.py", line 73, in _run_code
    exec(code, run_globals)
  File "e:\python-dev\py3k\lib\test\test_capi.py", line 182, in <module>
    test_main()
  File "e:\python-dev\py3k\lib\test\test_capi.py", line 143, in test_main
    support.run_unittest(CAPITest)
  File "e:\python-dev\py3k\lib\test\support.py", line 1127, in run_unittest
    _run_suite(suite)
  File "e:\python-dev\py3k\lib\test\support.py", line 1110, in _run_suite
    raise TestFailed(err)
test.support.TestFailed: Traceback (most recent call last):
  File "e:\python-dev\py3k\lib\test\test_capi.py", line 50, in test_no_FatalErro
r_infinite_loop
    b'Fatal Python error:'
AssertionError: b'Fatal Python error: PyThreadState_Get: no current thread\r\n\r
\nabnormal program termination' != b'Fatal Python error: PyThreadState_Get: no c
urrent thread'

This happens because "abnormal program termination" is output to
stderr. Another capable sink to output error message into is
messagebox, of cause it is not what we want. There is no way to
silent this.

I think there are a few options to take.
* Skip this test on VC6 (And probably VS7.1)
* Check not equality, but if stderr starts with "Fatal Python ...."