Summary:
This enables the following workflow:
```
$ ./build-infer.sh
[...]
$ opam upgrade # takes infer dependencies into account
```
To do so, we install a temporary `infer-deps-XXXX` package as before (the temp
name is because opam thinks there's nothing to do otherwise), then we install
an `infer-deps` package permanently.
Reviewed By: mbouaziz
Differential Revision: D4867195
fbshipit-source-id: da806f9
Jules Villard