This commit changes the general behavior from
'Retry on every exception and abort on DownloadError' to
'Only retry on DownloadRetry exceptions and abort on every other one'
The previous version would have retried on several states which
would have no chance of ever succeeding (invalid URLs, etc.)
This allows for image filtering via Python expressions by the same
metadata that is also used to build filenames (--list-keywords).
The usually shunned eval() function is used to evaluate
filter-expressions, but it seemed quite appropriate in this case and
shouldn't introduce any new security issues, as any attacker that could do
> gallery-dl --filter "delete-everything()" ...
could as well do
> python -c "delete-everything()"
Mike Fährmann