Handle very old YAJL without yajl_version method

old yajl versions don't have the yajl_version method and produce an AttributeError when importing ijson.

See the following backtrace:

ERROR: Failure: AttributeError (/usr/lib64/libyajl.so.1: undefined symbol: yajl_version)

   Traceback (most recent call last):
    .venv/contentpublisher-3.0.0-Linux/lib/python2.6/site-packages/nose/loader.py line 413 in loadTestsFromName
      addr.filename, addr.module)
    .venv/contentpublisher-3.0.0-Linux/lib/python2.6/site-packages/nose/importer.py line 47 in importFromPath
      return self.importFromDir(dir_path, fqname)
    .venv/contentpublisher-3.0.0-Linux/lib/python2.6/site-packages/nose/importer.py line 94 in importFromDir
      mod = load_module(part_fqname, fh, filename, desc)
    tests/__init__.py line 6 in <module>
      from contpublisher import requestmanager
    src/contpublisher/requestmanager.py line 32 in <module>
      from contpublisher import cdnmanager
    src/contpublisher/cdnmanager.py line 12 in <module>
      import ijson.backends.python as ijson
    .venv/contentpublisher-3.0.0-Linux/lib/python2.6/site-packages/ijson/__init__.py line 21 in <module>
      import ijson.backends.yajl2 as backend
    .venv/contentpublisher-3.0.0-Linux/lib/python2.6/site-packages/ijson/backends/yajl2.py line 14 in <module>
      yajl = backends.find_yajl(2)
    .venv/contentpublisher-3.0.0-Linux/lib/python2.6/site-packages/ijson/backends/__init__.py line 11 in find_yajl
      major, rest = divmod(yajl.yajl_version(), 10000)
    /usr/lib64/python2.6/ctypes/__init__.py line 366 in __getattr__
      func = self.__getitem__(name)
    /usr/lib64/python2.6/ctypes/__init__.py line 371 in __getitem__
      func = self._FuncPtr((name_or_ordinal, self))
   AttributeError: /usr/lib64/libyajl.so.1: undefined symbol: yajl_version