compound constituents not picklable

I'm trying to pickle the tide model object of pytides, but got error of "TypeError: can't pickle instancemethod objects" for compound constituents.
How can I fix this?

example code:

``` python
import cPickle as pickle
tide_dec=Tide.decompose(ds,tc)
with open(fname, 'w') as fmodel:
    pickle.dump(tide_dec.model,fmodel)
```
