libsmbconf: add a "path" variable to the conf context.

libsmbconf: add a "path" variable to the conf context.

This is passed to the module init routines.
In case of the registry, this is the path of the
basekey in registry, that is to be used, defaulting
to KEY_SMBCONF (HKLM\software\samba\smbconf), when
NULL is given. This is the only case currently used.

In order to support other keys, registry initialization
for smbconf has to be changed to support different keys.

Michael
(This used to be commit 96434d9dc7a66773e313cc128af57493dee245a1)