MFC r252414:
truss: recognize O_DIRECTORY, O_EXEC, O_TTY_INIT and O_CLOEXEC
Fix grammar in a comment.
MFC r250982: sigreturn(2): Remove ancient compatibility warning about 4.2BSD

The HISTORY subsection still says that sigreturn() was added in 4.3BSD.
MFC r251078,r251433: sleep: Improve nanosleep() error handling:

 * Work around kernel bugs that cause a spurious [EINTR] return if a
   debugger (such as truss(1)) is attached.

 * Write an error message if an error other than [EINTR] occurs.

PR:		bin/178664
MFC r251209: test(1): List non-standard primaries.
MFC r248692: sh(1): Mention possible ambiguities with $(( and ((.

In some other shells, things like $((a);(b)) are command substitutions.

Also, there are shells that have an extension ((ARITH)) that evaluates an
arithmetic expression and returns status 1 if the result is zero, 0
otherwise. This extension may lead to ambiguity with two subshells starting
in sequence.