Rework bucoord prototypes for external dlq use

Rework bucoord prototypes for external dlq use

Rework prototyping in the bucoord directory so that bucoord_prototypes.h
can be used by others who need definitions of the dlq_* types.
Add additional prototyping and header includes so these types work correctly

No Windows specific changes are required, as the NTMakefile doesn't have
header dependencies

Reviewed-on: http://gerrit.openafs.org/35
Verified-by: Russ Allbery <rra@stanford.edu>
Reviewed-by: Russ Allbery <rra@stanford.edu>