license cleanup

This patch cleans up the licensing terms on some imported BSD-licensed
files in the source tree:

- src/port/qsort.c is from NetBSD, and still contained the old 4-clause
BSD license. The NetBSD folks have updated the BSD licensing terms in
their CVS code, so I upgraded our copy to the latest CVS copy (I just
merged the licensing fixes, no other substantive changes were made).

- src/port/crypt.c is also from NetBSD, so I updated the licensing terms
in a similar fashion. I also merged another upstream change: a bunch of
static read-only arrays were const-ified.

- src/port/memcmp.c was imported from NetBSD, but whoever imported it
didn't also include the licensing terms (which is not good, needless to
say). I added the copyright blurb from the current version of the file
in NetBSD CVS.

There is a bunch more license cleanup of this kind that can be done, but
this is a start.

I was also going to update the licenses on files imported from FreeBSD,
but apparently they haven't bothered fixing their files to reflect the
3-clause Berkeley license. Of course the fact they haven't done this
doesn't matter (the license change applies anyway); do people think it
is worth modifying the licenses on these imported files anyway?

Barring any objections I intend to apply this patch on Tuesday.

-Neil