Implement the "bindingfile" attribute, exactly like the maven 2.0 castor plugin, to specify a castor binding file

This plugin does not allow for the "-binding-file" command-line parameter to the "org.exolab.castor.builder.SourceGenerator" class, which is necessary if you need to override the default type-to-class binding, most likely to avoid a duplicate class problem.

Fortunately, this is easy to fix. Just adding a check for the "bindingfile" attribute (named to match the same attribute in the maven 2.0 castor plugin) to add the "-binding-file" command-line parameter works perfectly fine.

Patch attached.