Driver mapping refactory.

VFS CHANGES:
- dmap table no longer statically initialized in VFS
- Dropped FSSIGNON svrctl call no longer used by INET

INET CHANGES:
- INET announces its presence to VFS just like any other driver

RS CHANGES:
- The boot image dev table contains all the data to initialize VFS' dmap table
- RS interface supports asynchronous up and update operations now
- RS interface extended to support driver style and flags

docs/UPDATING

@@ -1,3 +1,6 @@
+20100610:
+        /usr/src/etc/usr/rc updated: copy it (or merge it) to /usr/etc/rc.
+        /usr/src/etc/rc updated: copy it (or merge it) to /etc/rc.
 20100408:
         /usr/src/etc/usr/rc updated: copy it (or merge it) to /usr/etc/rc.
 20100318: