OpenBSD support

  Thanks to Timo Myyrä. He says:

  "OpenBSD doesn't define blksize_t and blkcnt_t so define them as 'long'. Not
   sure if this is correct but seems to work. Neither does OpenBSD have the
   timer functions so omit them on OpenBSD.  The tests need to be tweaked for
   OpenBSD too, its similar to darwin in this. Testing with other BSD's would
   be welcome to see if it its needed there as well.

   The funcall-getpw function seems to handle return values incorrectly.
   As result it would cause exception on OpenBSD with incorrect entries
   and not nil value as expected. The fix below works on OpenBSD but
   could use some testing on other platforms as well."

  ...we'll see if something breaks.