compiling on 1.4

[Michiel de Mare]

Since you can't compile out of the box on 1.4 (because of the newer JDBC
version) maybe it's a good idea to test for the JVM version that ant uses,
and to fail automatically with a helpful error message if it's 1.4. If you
need to use  1.4, you'll have to edit the source anyway, and the current
errors that you get when compiling on 1.4 are extremely unlikely to point
you in the right direction.