Add a new set of notes to a process core dump to store procstat data.

The notes format is a header of sizeof(int), which stores the size of
the corresponding data structure to provide some versioning, and data
in the format as it is returned by a related sysctl call.

The userland tools (procstat(1)) will be taught to extract this data,
providing additional info for postmortem analysis.

PR:		kern/173723
Suggested by:	jhb
Discussed with:	jhb, kib
Reviewed by:	jhb (initial version), kib
MFC after:	1 month
Don't leak lock when returning.

PR:		kern/177888
Submitted by:	Sven-Thorsten Dietrich <sven vyatta com>
MFC after:	1 week
Fix incomplete printf.

PR:		kern/177889
Submitted by:	Sven-Thorsten Dietrich <sven vyatta com>
MFC after:	1 week
DTrace: print() should try to resolve function pointers

Merge changes from illumos:

3675 DTrace print() should try to resolve function pointers
3676 dt_print_enum hardcodes a value of zero

Illumos Revision:	b1fa6326238973aeaf12c34fcda75985b6c06be1

Reference:
https://www.illumos.org/issues/3675
https://www.illumos.org/issues/3676

Obtained from:	Illumos
MFC after:	1 month
Fix the buffer-overflow-fixing fixes.

Pointy-hat to: me, for not realizing snprintf() is available in kernel.
Thanks to: jh, for bringing me the good news of snprintf(), Pawel Worach, for
           noting that the panic can be provoked in i386 and not in amd64