Allow mixed kernel/userspace architecture.

This is to allow building an image for a 64bit machine but with 32bit userspace.

Probably not a common usecase but ideal if you need to address more higher quantities of memory but cant migrate to a full 64bit userspace due to something like ruby eating twice as much memory.
Merge pull request #156 from jbergler/development

Allow mixed kernel/userspace architecture.
Add opts parameter to docker_daemon.