GridFS index fixed. codec_options argument for Database.command.

[IlyaSkriblovsky]

It is funny and sad at the same time, but GridFS were creating index with a typo in field name and nobody noticed that :)

Also, ensure_index removed from get_last_version because ASC+ASC index, created in __init__ is sufficient.

For the means of testing indexes creation, I've added codec_options argument to Database.command(). It can be used to make command() to return response as SON instead of plain dict.

[coveralls]

Coverage increased (+0.005%) to 95.587% when pulling 484c47a on IlyaSkriblovsky:fix-gridfs-index into 6225f42 on twisted:master.

[psi29a]

We now have conflicts... to be expected now with less inline callbacks.

[IlyaSkriblovsky]

Rebased and solved conflicts.

I've noticed also that adding codec_options to Database.command was unnecessary since it passes all its **kwargs to find_one(), so I just can use as_class=SON. But as_class is deprecated in PyMongo for a long time and codec_options just reflects PyMongo's API, so I suggest to leave it.

P.S.
(Btw, this relates to the discussion of hidden **kwargs in another PR ;) )

P.P.S.
More on **kwargs. Notice how I had to do command() call here: https://github.com/twisted/txmongo/blob/master/txmongo/collection.py#L193
I can't just write command("listCollections", filter={"name": self.name}) as I would like to do because command() uses kwargs twice: it adds them to command payload and also passes them to find_one(). So "filter" kwarg not only adds up to DB command, but also messes it up on lower level. I hope we will eventually clean and tidy all this kwargs magic :)

[coveralls]

Coverage increased (+0.005%) to 95.592% when pulling 6de2064 on IlyaSkriblovsky:fix-gridfs-index into d279627 on twisted:master.

[coveralls]

Coverage increased (+0.005%) to 95.592% when pulling 6de2064 on IlyaSkriblovsky:fix-gridfs-index into d279627 on twisted:master.

[coveralls]

Coverage increased (+0.005%) to 95.592% when pulling 6de2064 on IlyaSkriblovsky:fix-gridfs-index into d279627 on twisted:master.

[IlyaSkriblovsky]

@psi29a how do you feel you about this PR now?

[psi29a]

LGTM, merging.

[psi29a]

Agreed about the kwarg magic, it's dark band-aid stuff that we should move away from. I formally apologize for adding to it. ;)