The smb.conf manpage is missing the parameter:
idmap_ldb:use rfc2307 = yes|no
This should be added to 4.0 and later.
before we document it, can this please be converted into a normal parameter instead of a parametric option? We (Sama Team) even rcommneded to use testparm to clean up the smb.conf ... which is basically a good idea but not with neeedless parametric options all around :-/
Update: The parameter is still not documented in 4.5.0rc2.