MFC r258426: libexecinfo: Include terminating null in byte count

  Otherwise, a formatted string with a strlen equal to the remaining
  buffer space would have the last character omitted (because vsnprintf
  always null-terminates), and later the assert in backtrace_symbols_fmt
  would fail.

Sponsored by:	DARPA, AFRL
Approved by:	re (gjb)
MFC r258135: x86: Allow users to change PSL_RF via ptrace(PT_SETREGS...)

  Debuggers may need to change PSL_RF. Note that tf_eflags is already stored
  in the signal context during signal handling and PSL_RF previously could
  be modified via sigreturn, so this change should not provide any new
  ability to userspace.

  For background see the thread at:
  http://lists.freebsd.org/pipermail/freebsd-i386/2007-September/005910.html

  Reviewed by:	jhb, kib

Sponsored by:	DARPA, AFRL
Approved by:	re (gjb)