- 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

regression/date: unset all LC_xxx vars and set LANG/LC_ALL

When running with a custom locale setup, it's easy to confuse the
date regression tests and cause them to fail, e.g. when LANG='C'
but LC_ALL='el_GR.UTF-8'. Set LC_ALL to 'C', which overrides all
other LC_xxx options, to avoid this sort of problem.

Reviewed by: uqs, edwin

Use t1 & t2 as more symbolic than 'a' and 'b' for the two times.

Allow to be driven by 'prove -r'.

Add regression tests for the date(1) + argument for user-defined
format strings.

PR: bin/127514
Submitted by: edwin@
MFC after: 1 week