add method path_to_dn() to convert a given "path" to a DN
path_to_dn() replaces the occurrences of '~', '.' and '..' in a path given
and returns a DN.
However, it does not check whether the DN is valid.
Especially:
- on return it is not guaranteed that the DN exists
- on return the first part does not need to be a valid RDN
66ab8df0b6c8bb0dcb5dce8a7e8cd6a28e6c7c04 0.2
46dfe9d6f3680bf38aeddda68f014fc8bf6517fc 0.3
664bbe3dcd44e842559978725bf2128538a2b40a 0.4