Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

libkvm code janitoring

- make WARNS=6 clean for archs w/o strict alignment requirments
- add const, ANSIfy, remove unused vars, cast types for comparison
- thanks to differing definitions of VM_MIN_ADDRESS across our archs, we
need to trick the compiler to not complain about signedness. We could
either fix VM_MIN_ADDRESS to always be a simple integer or make the
check conditional on $ARCH.

Closes PRs: kern/42386, kern/83364
Reviewed by: bde

Fix missing includes of <string.h>, to silence some compiler warnings.

Submitted by: Pawel Worach

Add a new routine kvm_getcptime(3) for fetching the equivalent of
'kern.cp_time'. For a live kernel it uses the sysctl. For a crashdump,
it first checks to see if the kernel has a 'cp_time' global symbol. If
it does, it uses that. If that doesn't work, when it uses the recently
added kvm_getmaxcpu(3) and kvm_getpcpu(3) routines to walk all the CPUs
and sum up their counters.

MFC after: 1 week