Can't read tiles for dm5 gene annotations

Error:

```
----------------------------------------------------------------------
Traceback (most recent call last):
File "/Users/peter/projects/higlass-server/tilesets/tests.py", line 41, in test_to_string
tile = json.loads(self.client.get('/api/v1/tiles/?d=ga1.0.0').content)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/django/test/client.py", line 529, in get
**extra)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/django/test/client.py", line 333, in get
return self.generic('GET', path, secure=secure, **r)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/django/test/client.py", line 409, in generic
return self.request(**r)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/django/test/client.py", line 494, in request
six.reraise(*exc_info)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/django/core/handlers/exception.py", line 39, in inner
response = get_response(request)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/django/core/handlers/base.py", line 187, in _get_response
response = self.process_exception_by_middleware(e, request)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/django/core/handlers/base.py", line 185, in _get_response
response = wrapped_callback(request, *callback_args, **callback_kwargs)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/django/views/decorators/csrf.py", line 58, in wrapped_view
return view_func(*args, **kwargs)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/django/views/generic/base.py", line 68, in view
return self.dispatch(request, *args, **kwargs)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/rest_framework/views.py", line 474, in dispatch
response = self.handle_exception(exc)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/rest_framework/views.py", line 434, in handle_exception
self.raise_uncaught_exception(exc)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/rest_framework/views.py", line 471, in dispatch
response = handler(request, *args, **kwargs)
File "/Users/peter/.virtualenvs/hg-server/lib/python2.7/site-packages/rest_framework/decorators.py", line 52, in handler
return func(*args, **kwargs)
File "/Users/peter/projects/higlass-server/tilesets/views.py", line 303, in tiles
res = map(lambda x: generate_tile(x, request), tileids_to_fetch)
File "/Users/peter/projects/higlass-server/tilesets/views.py", line 303, in
res = map(lambda x: generate_tile(x, request), tileids_to_fetch)
File "/Users/peter/projects/higlass-server/tilesets/views.py", line 210, in generate_tile
rdb.set(tile_id, pickle.dumps(tile_value))
File "/Users/peter/.virtualenvs/hg-server/bin/../lib/python2.7/copy_reg.py", line 70, in _reduce_ex
raise TypeError, "can't pickle %s objects" % base.__name__
TypeError: can't pickle buffer objects
```