1.0.28.66: implement SB-EXT:GET-TIME-OF-DAY

1.0.28.66: implement SB-EXT:GET-TIME-OF-DAY

 * On unixoid platforms is this pretty much what UNIX-GETTIMEOFDAY
   used to be, whereas on Windows we build it on top of
   SystemTimeAsFileTime since gettimeofday() doesn't give us
   microseconds there -- it's almost as if the POSIX API support on
   Windows as intentionally sucky...

 * Keep UNIX-GETTIMEOFDAY around as a wrapper to GET-TIME-OF-DAY,
   since there are applications in the wild that use it directly.
   Scheduled for deletion towards to the end of 2009, or so.