`keybase decrypt` intermingled info lines about identity with the actual message

I just ran a `keybase decrypt` command with a message authored by @maxtaco, and the decrypted message was printed in the middle of the info lines about his identity.

```
> pbpaste | keybase decrypt
▶ INFO Message authored by max; identifying...
✔ public key fingerprint: 8EFB E2E4 DD56 B352 7363 4E8F 6052 B2AD 31A6 631C
฿ bitcoin 1BYzrCvfbn81dfiksmD1Bdgt8pgLi1SD7Z
REDACTED MESSAGE WAS HERE✔ "maxtaco" on github: https://gist.github.com/8847250 [cached 2016-02-04 19:43:54 PST]
```

In #1897 he says the info lines are going to stderr and the output is going to stdout, which is fine, but the tool should still probably serialize it so the info lines are printed (and flushed) prior to printing the output.

I'm also a bit confused as to why it printed his bitcoin and his github identity, but nothing else. It's almost as if it started asynchronously printing proofs, but only printed 2 of them before it finished decrypting and exited.

Start at the `keybase decrypt` command and compare its stderr identity-proof reporting with stdout message output, using #1897 for the stream behavior described here. Done means the identity and proof information is serialized and flushed before the decrypted message, with the observed bitcoin and GitHub proof behavior explained.

Written by the indexing model from the issue text.