Add patches from Aymeric Vincent to fix sb-posix on recentish NetBSD.

Add patches from Aymeric Vincent to fix sb-posix on recentish NetBSD.

There is some possibility that this will break one of the sb-posix tests on FreeBSD:

  The "rmdir" patch needs some input from FreeBSD users.
  "rmdir /" returns EBUSY on NetBSD. Given the recent commit
  2a9b33fc45842ec0335fef2988e07337ae8f1fc7 on october, 17. 2011, it looks
  like OpenBSD and Darwin return EISDIR, but it's clearly not the case of
  NetBSD with a (usual) FFS file system.

  In short, either sbcl is currently broken on FreeBSD wrt the rmdir test
  and my patch will fix it, or my patch will break it and we need to include
  freebsd in the list of OSes producing EISDIR upon "rmdir /".