- 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

Added the EXIT STATUS section where appropriate.

mdoc(7) police: markup polishing.

Approved by: re

Note that this appeared at least as early as PWB UNIX.

Use the literal string 'PWB UNIX', as we still have no .At macro for it.

Use the Tn macro for COBOL, FORTRAN, PL/1, SNOBOL.

Support the "--" end-of-options marker.

Expand description of environment variables, refer to environ(7) where
appropriate.

mdoc(7) police: pedantry.

Mark argc as __unused to silence GCC.

Add an implementation of the tabs(1) utility, as required by SUSv3.

PR: 36126