Sorry, I did a little of confusion.

1) update this pull request: remove `2.0.0-alpha2` and add `dev-master` so that in PropelServiceProvider's `composer.json` there'll be:
``` json
"propel/propel": "dev-master"
```
2) When it'll be merged, in your project's `composer.json` write:
``` json
"require": {
    "propel/propel-service-provider": "2.x"
}
```
and it'll install a Propel2 compatible version of PropelServiceProvider and Propel2 master branch.