Backport Superuser from CM10.1

Edited to remove multiuser code, otherwise it's the same as CM10.1

Not all devices are capable of runing CM10.1, so it makes sense to
bring the security advantages of this back a generation.

Edits to the Superuser app can be found at:

https://github.com/adfad666/Superuser
https://github.com/adfad666/Widgets

Change-Id: Id7e29b2b87c33102fa0ebad3cc78c43cb6a2f76d