r9894: Add new registry key expected by Windows XP clients.

r9894: Add new registry key expected by Windows XP clients.

  HKLM\\SYSTEM\\CurrentControlSet\\Control\\Termininal Server\\DefaultUserConfiguration

Apparently this started showing up after the winreg-write support
was added in 3.0.20rc1 or so.

Also modifed init_registry_data() to always run and add the
required keys.  Initial values however are only written if
they don't already exist.

This makes it easier to add new keys without having to rev the
tdb version number (which is really unnecessary in this case).

Portions of patch reviewed by Thomas Bork on the general samba ml.