Fixes GoogleCloudPlatform/google-cloud-go#419.

sed's -i flag differs on platform. Switch based on platform.

(Also moved api/distribution which had ended up in the wrong spot).

Fixes #5

Add back the appengine API.

These files now appear as sub-packages in the rpc and type directories.

Split up the rpc directory into its individual components.
Disable three APIs known to be currently broken in the upstream repo.

The proto files within are dervied from:
  https://github.com/google/protobuf
  https://github.com/googleapis/googlapis