JdbcStorage update

JdbcStorage has been broken for a while due to build changes and changes 
to the MDRCache class which JdbcStorage borrows from BTreeStorage.  I 
just checked in fixes so it should build and run again.  I also fixed 
some other bugs I found in my code.

I'm finding that JdbcStorage with the latest release of HSQLDB running 
in-process appears to be even a little faster than BTree storage.  This 
is just from casual observation with small data sets.  But it raises the 
question:  instead of continuing to put effort into the BTree library 
(e.g. enhancing with java.nio), why not replace it with an embedded Java 
database instead?  HSQLDB uses java.nio already, and supports both 
memory-based and disk-based tables.  Its license recently changed to 
new-BSD (the old advertising clause was removed) which is compatible 
with just about anything.  They claim performance has improved a lot, 
and it has crash recovery.

Or if something more robust is required, there's Derby nee Cloudscape. 
I haven't tried it yet.

JVS