This patch fixes 3 small problems.
1) If a map is used which is generated with 'makedbm -a',
   the trailing '\0' is now handled correctely.
2) The nis.maps() function skipped the first map in the output list.
3) The library '-lnsl' is added in Setup.in (needed on Linux glibc2 and
   Solaris systems. Maybe on other systems too?)

[I note that this still doesn't work when you are using NIS+ --GvR]