[Feature request]: take priorities into account in sequential mode.

[alervd]

Please take a look at this torrent:
magnet:?xt=urn:btih:DA9CE19D26A9B95A6D619AB11954529A742C4F6B&tr=http%3A%2F%2Fbt.t-ru.org%2Fann%3Fmagnet.

It contains 6 seasons of TV series.

Let's suppose the user wants to download it and also wants to start watching the first episode (s01e01) as soon as possible (even before it's fully downloaded). For this, he would choose sequential mode and set s01e01 to high priority. Unfortunately, this does not work and Libtorrent downloads s06e20 instead. This is because this file is located at the "beginning" of the torrent.

What I would like is for Libtorrent to be able to take priorities into account in sequential mode too. For this, it sequentially downloads pieces with higher priorities first, then sequentially downloads pieces with lower priorities.