Warn if several complex properties with the same name are defined in different schemas

If several schemas use complex types with the same name and different definitions, a WARN (at least) should be emitted because only a single table will be used and there will be collision of these types.

For instance this is the case for the "name" field of complex property "property" of these two schemas:

• https://github.com/nuxeo/nuxeo-opensocial/blob/5.6.0/nuxeo-opensocial-spaces/src/main/resources/schemas/wcopensocial.xsd
• https://github.com/nuxeo/nuxeo-opensocial/blob/5.6.0/nuxeo-opensocial-spaces/src/main/resources/schemas/gadget.xsd