More mult-user API work.

- You can now use android:singleUser with receivers and providers.
- New API to send ordered broadcasts as a user.
- New Process.myUserHandle() API.

For now I am trying out "user handle" as the name for the numbers
representing users.

Change-Id: I754c713ab172494bb4251bc7a37a17324a2e235e
25 files changed