- 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

Add unistd.h to the getosreldate(3) manpage.
Update referenced example to include unistd.h per manpage.
Update example to be more style(9)-ish, silence warnings and add
FreeBSD id to the source file.

Remove trailing whitespace.

Added example of how to tell various FreeBSD versions apart.