more build changes

[Rick Hillegas]

I am simplifying the way that the Derby build sets the classpath 
properties. Once again I need your help in test-driving a patch: 
derby-5485-01-ag-changeJDBClevel.diff attached to DERBY-5485. In 
particular, I need volunteers to test-drive that patch and verify that 
the build works correctly in the following environments:

o Oracle JDKs on Windows
o IBM JDKs on Windows

Thanks,
-Rick