- 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

Fix 'make release' on older hosts: use buildworld legacy utilities.

Newer FreeBSD installs require an install(1) that supports the new flags.

This adds ${MAKEOBJDIRPREFIX}${.CURDIR}/tmp/legacy/{bin,usr/{bin,sbin}}
to the PATH while generating an mtree database for 'make release'.

Note that the problem only exists here because mm-mtree.sh generates
its own object tree to avoid mucking with the existing one, which
results in a PATH containing legacy utility dirs that are empty.

Add a script to create the /var/db/mergemaster.mtree file for new
releases so that when users subsequently update their source trees
they can make use of mergemaster's -U option.