r20221: - move the dsdb_schema, dsdb_attribute, dsdb_class structs into

r20221: - move the dsdb_schema, dsdb_attribute, dsdb_class structs into
  a generic location
- this struct should be also used by the dsdb/samdb/ldb_modules/schema.c
  module later
- add functions to map from LDAP OID values to uint32_t values
- add torture test for the OID => uint32 mapping code

metze
(This used to be commit 58ba6ec195ce3a5e2352866809f6cb57f8d8260a)