- Copy stable/10 (r259064) to releng/10.0 as part of the
10.0-RELEASE cycle.
- Update __FreeBSD_version [1]
- Set branch name to -RC1

[1] 10.0-CURRENT __FreeBSD_version value ended at '55', so
start releng/10.0 at '100' so the branch is started with
a value ending in zero.

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

Renumber clauses to reduce diffs to other versions

NetBSD, OpenBSD, and Android's Bionic number the clauses 1 through 3,
so follow suit to make comparison easier.

Implement strndup(3) using strnlen(3).

This makes the implementation a bit more consistent with strdup(3),
which uses strlen(3).

Import the strndup(3) function.
Copyright attribution is kept the same as in original NetBSD source.

Submitted by: Florian Smeets <flo kasimir com>
Obtained from: NetBSD
MFC after: 2 weeks