r13545: A patch which I think it's time has come. VOlker, we can talk about

r13545: A patch which I think it's time has come.  VOlker, we can talk about
this more but it gets around the primary group issue.

* don't map a SID to a name from the group mapping code if
  the map doesn't have a valid gid.  This is only an issue
  in a tdb setup
* Always allow S-1-$DOMAIN-513 to resolve (just like Windows)
* if we cannot resolve a users primary GID to a SID, then set
  it to S-1-$DOMAIN-513
* Ignore the primary group SID inside pdb_enum_group_memberships().
  Only look at the Unix group membersip.

Jeremy, this fixes a fresh install startup for smbd as far as my tests
are concerned.
(This used to be commit f79f4dc4c58a6172bf69d37469fdd8de05a812df)