Add Retry button to one of the extraction dialog's prompts.

As written by the patch author:
With this patch, there will be a working Retry button on the dialog
box made in ExtractionDialog::accept().

This implements an old TODO item written by Harald a few years ago
(commit f761cbd164c1015100d810ec3c02a60b78969891), and users are now
able to retry when an extraction into a subdirectory will overwrite an
existing location.

Submitted by: Nathan Mills
REVIEW: 104869