Flesh out sysctl types further (follow-up of r290475)

Use the right intmax_t type instead of intptr_t in a few remaining
places.

Add support for CTLFLAG_TUN for the new fixed with types. Bruce will be
upset that the new handlers silently truncate tuned quad-sized inputs,
but so do all of the existing handlers.

Add the new types to debug_dump_node, for whatever use that is.

Bump FreeBSD_version again, for good measure. We are changing
SYSCTL_HANDLER_ARGS and a member of struct sysctl_oid to intmax_t.

Correct the sysctl typed NULL values for the fixed-width types. (Hat
tip: hps@.)

Suggested by: hps (partial)
Sponsored by: EMC / Isilon Storage Division