We could just remove the "dup: 1" part in the completion dict, but that would
leave the duplicate removal up to Vim which would be slow. Also, we might not
end up returning the correct number of results then.
By toggling the g:ycm_seed_identifiers_with_syntax option, the user can now tell
YCM to seed the identifier database with the language's keywords.
This is off by default because it can be noisy. Since the identifier completer
collects identifiers from buffers as the user visits them, the keywords that the
user cares about will already be in the database, regardless of the state of the
new option. So the only keywords added will be the ones the user is not using.
Meh. But people want it so there.
Fixes#142.
