this is a trick to work around the fact that posix does not supply

this is a trick to work around the fact that posix does not supply
a getgr*() function that lists groups without numerating all the
group members. Instead of definiing a new nss method (which might
cause problems) I added an environment variable WINBIND_GETGRLST
that tells winbind not to fill in the group members in a gergrent()
request. This can speed up group listing by a factor of 20 or more
(on my test system with 50000 groups it reduces the time from an hour
to 2 minutes)