[Hibernate] Normalized table mappings

[Gavin K. <ga...@ap...>]

I now have what I believe is a fully-working implementation of the
table-per-subclass mapping strategy. It would be really cool if people would
try it out. I plan to release this new feature as Hibernate 1.2 beta. The
only missing thing is support for databases without ANSI-style OUTER JOIN
and CASE. So we'll still need to do a bit more work to get it working on
Oracle.

At this point I'm deprecating hibernate-mapping.dtd and documenting
hibernate-mapping-1.1.dtd as the preferred mapping document DTD. Theres a
couple of non-compatible changes, but nothing that should cause headaches.