test_add_archive_use_archive_dir() uses expression that is broken on windows

[mih]

[00:04:01] ======================================================================
[00:04:01] ERROR: datalad.interface.tests.test_add_archive_content.test_add_archive_use_archive_dir
[00:04:01] ----------------------------------------------------------------------
[00:04:01] Traceback (most recent call last):
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\site-packages\nose\case.py", line 198, in runTest
[00:04:01]     self.test(*self.arg)
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\site-packages\datalad\tests\utils.py", line 1138, in newfunc
[00:04:01]     reraise(*exc_info)
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\site-packages\six.py", line 693, in reraise
[00:04:01]     raise value
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\site-packages\datalad\tests\utils.py", line 1114, in newfunc
[00:04:01]     func(*args, **kwargs)
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\site-packages\datalad\tests\utils.py", line 499, in newfunc
[00:04:01]     return t(*(arg + (d,)), **kw)
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\site-packages\datalad\interface\tests\test_add_archive_content.py", line 346, in test_add_archive_use_archive_dir
[00:04:01]     str(cmr.exception), match=False
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\site-packages\datalad\tests\utils.py", line 1176, in assert_re_in
[00:04:01]     if (re.match if match else re.search)(regex, e, flags=flags):
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\re.py", line 173, in search
[00:04:01]     return _compile(pattern, flags).search(string)
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\re.py", line 293, in _compile
[00:04:01]     p = sre_compile.compile(pattern, flags)
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\sre_compile.py", line 536, in compile
[00:04:01]     p = sre_parse.parse(p, flags)
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\sre_parse.py", line 829, in parse
[00:04:01]     p = _parse_sub(source, pattern, 0)
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\sre_parse.py", line 437, in _parse_sub
[00:04:01]     itemsappend(_parse(source, state))
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\sre_parse.py", line 524, in _parse
[00:04:01]     code = _escape(source, this, state)
[00:04:01]   File "C:\Miniconda35\envs\test-environment\lib\sre_parse.py", line 418, in _escape
[00:04:01]     raise source.error("invalid group reference", len(escape))
[00:04:01] sre_constants.error: invalid group reference at position 33