[BioPython] GenBank feature proprotein

[Bertrand FROTTIER]

Hello everyone !

I recently wrote a simple program to get sequences from GenBank.
It's working fine for most of the sequences but failed for 5 of them 
(NM_001565, NM_001710, NM_006332, NM_000245 and NM_000212 if you're 
curious).
After having a look at the records, I discovered that they all have in 
common a new *undocumented* feature: "proprotein".
Fortunately, the fix is rather simple: simply add a key "proprotein" in 
Bio.GenBank.genbank_format feature_key_names, and everything is working 
fine !

Hope this helps.

Cheers,

Bertrand