use RFC5987 encoding for filenames

[minrk]

as described in RFC 6266 describing Content-Disposition

This should result in the correct download filename for filenames with spaces and non-latin characters

finishes up #2761
closes #2742

[minrk]

Hold the phone, this doesn't work on Firefox, which apparently doesn't implement RFC 5987 the same as other browsers

works on FF

[takluyver]

On #2761 you said you've tested this on Firefox. Does that supersede your comment here that it doesn't work?

[minrk]

@takluyver yes, sorry. Commenting in two issues. My first attempt didn't work on Firefox, but it does now.

[takluyver]

Thanks. Confirmed with a manual test.

I'd be in favour of putting this in 5.1, but if we're not confident enough it's fine to bump it to 5.2.

[minrk]

It worked for me, but the tiniest typo while I was figuring this out caused pretty weird failures that different browsers handled differently, so I'd be okay merging right after 5.1.

[gnestor]

I tested and I'm still seeing filenames with pluses vs. spaces?

[gnestor]

Ok, nevermind. I guess that I was not using a develop version of notebook or something. Looks good to me!

@minrk What do you think about merging this with 5.1 now? Feel free to mark as 5.2 otherwise.

[minrk]

Let's be conservative and call it 5.2