too specific for a general API.
* Implemented {Register,Unregister}FileDevice().
* Implemented Get{Device,Partition}WithID() and
Get{Device,Partition}ForPath().
git-svn-id: file:///srv/svn/repos/haiku/trunk/current@3979 a95241bf-73f2-0310-859d-f6bbb57e9c96