from RELENG_4 until issue is resolved in 5.0-CURRENT.

This will make a number of things easier in the future, as well as (finally!)
avoiding the Id-smashing problem which has plagued developers for so long.

Boy, I'm glad we're not using sup anymore.  This update would have been
insane otherwise.

- getservent:
  o put _yp_check() proto under #ifdef YP where it belongs
  o local YP buffers should be YPMAXRECORD + 2 bytes long and should
    be NUL terminated after copying

- gethostbynis:
  o local YP buffer should be YPMAXRECORD + 2 bytes long

- getnetbynis:
  o local YP buffer should be YPMAXRECORD + 2 bytes long and should
    be NUL terminated after copying

- ether_addr:
  o local YP buffers should be YPMAXRECORD + 2 bytes long and should
    be NUL terminated after copying (in this case it's BUFSIZ + 2 bytes,
    but it happens that BUFSIZ == YPMAXRECORD.

- gethostbydns:
  o nuke stray 'return(NULL)' in __dns_getanswer() (harmless but looks silly)

These are 2.2 candidates. I will wait a few days to make sure these don't
break anything and then, if there are no objections, move them to the 2.2
branch.

in lots of unrelated junk from <net/if.h> and <net/if_ether.h>.  These
functions still aren't prototyped anywhere (but should be in
<net/ethernet.h>---got that, Bill?).