These changes take advantage of the newly-added support for returning
inputs from Read to update a resource's inputs as part of a refresh.
As a consequence, the Pulumi engine will now properly detect drift
between the actual state of a resource and the desired state described
by the program and generate appropriate update or replace steps.
As part of these changes, a resource's old inputs are now passed to the
provider when performing a refresh. The provider can take advantage of
this to maintain the accuracy of any additional data or metadata in the
resource's inputs that may need to be updated during the refresh.
This is required for the complete implementation of
https://github.com/pulumi/pulumi-terraform/pull/349. Without access to
the old inputs for a resource, TF-based providers would lose all
information about default population during a refresh.
These changes add a new resource to the Pulumi SDK,
`pulumi.StackReference`, that represents a reference to another stack.
This resource has an output property, `outputs`, that contains the
complete set of outputs for the referenced stack. The Pulumi account
performing the deployment that creates a `StackReference` must have
access to the referenced stack or the call will fail.
This resource is implemented by a builtin provider managed by the engine.
This provider will be used for any custom resources and invokes inside
the `pulumi:pulumi` module. Currently this provider supports only the
`pulumi:pulumi:StackReference` resource.
Fixes#109.
