Fix GET /extras error when title has non ascii characters

The error is this:

2014-03-28 22:52:52,981 INFO  [cnxarchive][Dummy-1] GET - /extras/2ab14729-a046-45b0-a91e-2d610097689d@1
2014-03-28 22:52:53,002 ERROR [cnxarchive][Dummy-1] Unknown exception
Traceback (most recent call last):
  File "/home/karen/cnx-archive/cnxarchive/__init__.py", line 94, in __call__
    return controller(environ, start_response)
  File "/home/karen/cnx-archive/cnxarchive/views.py", line 322, in get_extra
    exports_dirs, id, version))
  File "/home/karen/cnx-archive/cnxarchive/views.py", line 111, in get_export_allowable_types
    id, version, type_name, exports_dirs)
  File "/home/karen/cnx-archive/cnxarchive/views.py", line 150, in get_export_file
    version, file_extension)
UnicodeEncodeError: 'ascii' codec can't encode character u'\xf8' in position 12: ordinal not in range(128)
Merge pull request #206 from Connexions/fix-utf8-filename

Fix GET /extras error when title has non ascii characters