Add PRIV_FATAL privilege check to kern_fatal() system call

Signed-off-by: Alex Smith <alex@alex-smith.me.uk>
allocstats: Exclude slab internal caches from results by default

Allocations from some slab internal caches may be outstanding in the
results, these aren't necessarily leaks so hide them by default.

Signed-off-by: Alex Smith <alex@alex-smith.me.uk>
Move some kern_process_{create,exec}() args to optional attributes structure

The argument count for kern_process_{create,exec}() was getting a bit big
and they're about to get another argument for IPC-related stuff). For the
majority of uses these arguments aren't needed (e.g. there are only a few
places where something would need to specify a new security token or root
port when creating a new process). Moved the less frequently needed
arguments to an optional process_attrib_t structure. If the structure
pointer is given as NULL, then default behaviour for all of its members
is used.

Signed-off-by: Alex Smith <alex@alex-smith.me.uk>