r2832: Readd WKGUID-binding to match the correct default-locations of new

r2832: Readd WKGUID-binding to match the correct default-locations of new
User-, Group- and Machine-Accounts in Active Directory (this got lost
during the last trunk-merge).

This way we match e.g. default containers moved by redircmp.exe and
redirusr.exe in Windows 2003 and don't blindly default to cn=Users or
cn=Computers.

Further wkguids can be examied via "net ads search wellknownobjects=*".
This should still keep a samba3-client joining a samba4 dc. Fixes
Bugzilla #1343.

Guenther