Port t_pipe2.c to FreeBSD

- Omit the pipe2_nosigpipe testcase on FreeBSD (FreeBSD doesn't have
  O_NOSIGPIPE).
- Convert "fcntl(n, F_CLOSEM)" to "closefrom(n)".
- Save and restore the resource limit on the number of files (RLIMIT_NOFILE).

In collaboration with: pho
Sponsored by: EMC / Isilon Storage Division
Convert "fcntl(n, F_CLOSEM)" to "closefrom(n)"

Submitted by: pho
Sponsored by: EMC / Isilon Storage Division