Support FileSets in CompileTask Ant task

Currently, the CompileTask Ant task configuration (sources, externals, etc.) support only FileLists. These require every single file to be named explicitly, which is a lot of unnecessary maintenance.

It would be much better to support FileSets instead (or in addition), so one can specify e.g. .js in a source directory (or even **/.js for well-organized external scripts) to pick up all the files automatically without having to change the script.

The current workaround is to have a separate task to create a fixed-name temporary file with the concatenated contents of all he required files (per configuration item), pass that to the CompileTask explicitly, and then erase the temporary file. It's a lot of unnecessary maintenance complexity either way.

Thanks!