Add source reference information for merged packages

[webflo]

Attempt to fix #101

[mikkeschiren]

Real good work @webflo, seems to work very well, this is my composer.json:

{
    "name": "nodeone/wkse",
    "description": "Installation profile for wkse",
    "type": "drupal-profile",
    "minimum-stability": "dev",
    "repositories": [
      {
      "type": "package",
        "package":
          {
            "name": "md-systems/pathauto",
            "type": "drupal-module",
            "version": "8.1.0",
              "source": {
                "url": "https://github.com/md-systems/pathauto.git",
                "type": "git",
                "reference": "a38509d"
              }
          }
      },
      {
        "type": "composer",
        "url": "https://packagist.drupal-composer.org"
      }
    ],
    "require": {
        "drupal/devel": "dev-8.x-1.x#d913e1d",
        "drupal/config_devel": "dev-8.x-1.x#d4cdd21",
        "md-systems/pathauto": "^8.1",
        "drupal/token": "dev-8.x-1.x#d6cd94f19b053d8b6a411cb8fc5e75112d141d77",
        "drupal/memcache": "8.2.*@dev"
    }

And this was the result:

Updating dependencies (including require-dev)
  - Installing md-systems/pathauto (8.1.0)
    Cloning a38509d

  - Installing drupal/devel (dev-8.x-1.x d913e1d)
    Cloning d913e1d

  - Installing drupal/config_devel (dev-8.x-1.x d4cdd21)
    Cloning d4cdd21

  - Installing drupal/token (dev-8.x-1.x d6cd94f)
    Cloning d6cd94f19b053d8b6a411cb8fc5e75112d141d77

  - Installing drupal/memcache (dev-8.x-2.x 222f62f)
    Cloning 222f62f7c462f084d7d1852f747e0bf7e16909ca

[webflo]

@bd808 setReferences is not part of the RootPackageInteface. Should we use unwrapIfNeeded or should we try to fix it upstream?

[bd808]

I'd say that both are wanted. At the very least unwrapIfNeeded will cast or provide access to the aliased RootPackage. Upstreaming interface additions and tests is always a good idea I think. See composer/composer@06c44ce for an example of us doing this previously.

[bd808]

Commits should be squashed and rebased on current master.

[LionsAd]

FWIW, The patch looks great to me!