Per-priority endgame

[jakaj]

As far as I can tell, Transmission engages endgame based on total remaining bytes to download.

This means that if you have a single high-priority file, and others with normal priority, you'll be waiting for the high-priority file longer than needed.

I propose a per-priority endgame and am willing to put some effort into it, if you think it's a good idea.

[jordan]

This would be a nice-to-have feature if it doesn't make peer-mgr.c's code too much more convoluted. Prioritization is already kind of ugly as it is... :)