Update build script to Subversion

Helma's build script needs to be updated to reflect the move from the CVS repositories to Subversion.

Some things to consider:

• Currently the Helma build.xml script uses the <cvs> tags for adding additional packages in various places.
• Ant amazingly does not support Svn out of the box. There are some add-on packages to make ant support Svn, but it would be preferrable to avoid dependencies for non-standard ant tasks.
• svn:externals definitions in Subversion may be the way to go, checking out/exporting dependencies right away rather than at build time.

Current usage of <cvs> tag in Helma's build.xml