title: cryptography AssertionError: sorry, but this version only supports 100 named groups
body: <p>I'm installing several python packages via <code>pip install</code> on travis, </p>
  
  <pre><code>language: python
  python:
  - '2.7'
  install:
  - pip install -r requirements/env.txt
  </code></pre>
  
  <p>Everything worked fine, but today I started getting following error:</p>
  
  <pre><code> Running setup.py install for cryptography
  Traceback (most recent call last):
    File "&lt;string&gt;", line 1, in &lt;module&gt;
    File "/tmp/pip-build-hKwMR3/cryptography/setup.py", line 334, in &lt;module&gt;
      **keywords_with_side_effects(sys.argv)
    File "/opt/python/2.7.9/lib/python2.7/distutils/core.py", line 111, in setup
      _setup_distribution = dist = klass(attrs)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/setuptools/dist.py", line 269, in __init__
      _Distribution.__init__(self,attrs)
    File "/opt/python/2.7.9/lib/python2.7/distutils/dist.py", line 287, in __init__
      self.finalize_options()
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/setuptools/dist.py", line 325, in finalize_options
      ep.load()(self, ep.name, value)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/setuptools_ext.py", line 181, in cffi_modules
      add_cffi_module(dist, cffi_module)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/setuptools_ext.py", line 48, in add_cffi_module
      execfile(build_file_name, mod_vars)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/setuptools_ext.py", line 24, in execfile
      exec(code, glob, glob)
    File "src/_cffi_src/build_openssl.py", line 81, in &lt;module&gt;
      extra_link_args=extra_link_args(compiler_type()),
    File "/tmp/pip-build-hKwMR3/cryptography/src/_cffi_src/utils.py", line 61, in build_ffi_for_binding
      extra_link_args=extra_link_args,
    File "/tmp/pip-build-hKwMR3/cryptography/src/_cffi_src/utils.py", line 70, in build_ffi
      ffi.cdef(cdef_source)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/api.py", line 105, in cdef
      self._cdef(csource, override=override, packed=packed)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/api.py", line 119, in _cdef
      self._parser.parse(csource, override=override, **options)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/cparser.py", line 299, in parse
      self._internal_parse(csource)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/cparser.py", line 304, in _internal_parse
      ast, macros, csource = self._parse(csource)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/cparser.py", line 260, in _parse
      ast = _get_parser().parse(csource)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/cffi/cparser.py", line 40, in _get_parser
      _parser_cache = pycparser.CParser()
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/pycparser/c_parser.py", line 87, in __init__
      outputdir=taboutputdir)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/pycparser/c_lexer.py", line 66, in build
      self.lexer = lex.lex(object=self, **kwargs)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/pycparser/ply/lex.py", line 911, in lex
      lexobj.readtab(lextab, ldict)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/site-packages/pycparser/ply/lex.py", line 233, in readtab
      titem.append((re.compile(pat, lextab._lexreflags | re.VERBOSE), _names_to_funcs(func_name, fdict)))
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/re.py", line 194, in compile
      return _compile(pattern, flags)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/re.py", line 249, in _compile
      p = sre_compile.compile(pattern, flags)
    File "/home/travis/virtualenv/python2.7.9/lib/python2.7/sre_compile.py", line 583, in compile
      "sorry, but this version only supports 100 named groups"
  AssertionError: sorry, but this version only supports 100 named groups
  </code></pre>
  
  <p>Solutions?</p>