- 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

Repo-copy tools/regression/usr.bin/make to tools/build/make_check
and adjust the path in the Makefile for the upgrade_checks target.
These checks are really feature upgrade checks that should be fast
and just find out whether we need to build a new make before
proceeding with other targets like buildworld. This makes the
place free for a real regression test suite in the old place.

Make the tests runnable on a read-only src. To do this you must make sure
that you create one of the object directories make knows (see make(1)).
This uses the -C flag, so add a test that checks that make actually accepts
-C. Also fix the test that selects csh via the .SHELL target to work for
tcsh users too.

This commit renames shell_test to shell_test.sh. There is no history
to preserve so go without a repo-copy.

Reviewed by: ru