fix incorrect FFI binding for pubkey_combine

[apoelstra]

Fixes #669.

Needs backport.

[tcharding]

I rekon if we are going to backport this would be nicer have a bit more description in the commit log.

ACK 484e5d8

[apoelstra]

The one line commit log, combined with the one line diff, seem pretty self explanatory to me.

[Kixunil]

ACK 484e5d8

[apoelstra]

Would one or both of you @tcharding @Kixunil like to be a maintainer on this repo?

I think our informal processes are fine to make sure that e.g. crypto stuff doesn't get merged without a crypto person reviewing. There's no reason to use Github to only allow a narrower set of reviewers.

I'll go ahead and merge this with just your ACKs since we're not actually even enforcing the "maintainer must ACK" rule here..

[apoelstra]

Lol, oops, I actually screwed up this PR. I updated the secp-sys version but did not re-run the vendoring script to rename all the 0_9_1 functions to 0_9_2.

[Kixunil]

Yeah, I'd like to help maintain this. It's a key piece of the rust-bitcoin infrastructure so being more involved with it should help.

[Kixunil]

ACK 3373cc9

[apoelstra]

Thanks! Added you as a maintainer.

[apoelstra]

Tagged, published, and yanked previous 0.9.x versions of secp-sys.

[apoelstra]

Oops, crap, I need to update rust-secp along with rust-secp-sys, since this was actually a breaking change to rust-secp-sys.

[tcharding]

I'm willing to be a maintainer also. I'm not super confident with unsafe but willing to invest the time and take the responsibility.

[apoelstra]

Bumped you from "Triage" to "Maintain".