Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

The last big commit: let usr.sbin/ use WARNS=6 by default.

Give a major overhaul to asf(8).

The improvements are:

- can get the kld info from core files via kvm(3);
- can use kldstat(2) directly, which is a piece of cake;
- can use .symbols or whatever, which allows for use by
non-developers when reporting system crashes -- now asf(8)
can be mentioned in the handbook at last;
- speed (no more double fts(3) per loaded module);
- various bugs fixed.

At the same time, the new asf(8) should stay compatible with
the old one, bar bugs. Perhaps some defaults may be changed
later to match today's state of affairs.

Reviewed by: grog
MFC after: 1 month
Sponsored by: RiNet (Cronyx Plus LLC)

Use implicit SRCS list, remove WARNS=0, the code is WARNS=4 clean now,
which is more than enough.

Introducing asf, a helper program for kernel debugging.