More warnings cleanup for vol/

More warnings cleanup for vol/

Prototype a number of functions
Add additional includes as required
Make some existing prototypes match the actual declarations
Volume IDs are unsigned in most of the code, change this bit to match
Make various Procs take an anonymous pointer, so they can be type checked
Add vol_internal.h for prototypes internal to this package

Reviewed-on: http://gerrit.openafs.org/235
Tested-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>