Batch operation cancel dialog

[ImpulseAdventure]

The batch processing operation may be lengthy and there is no ability for the user to cancel the process.

I have already added the necessary code for a Progress dialog with cancel (OperationDlg), but it is only really suited for single-stepped algorithms, not recursion. The batchProcess() call is written with recursion to support descending into subdirectories.

[2010/11/14] First created at https://sourceforge.net/p/jpegsnoop/feature-requests/34/