Iteratively cover one loss lot at a time

[mag1024]

The old code was trying to batch-match all sales on a given day, with eligible buys.
This had several problems:

1. The buys were selected to be eligible to cover the first loss only. Other losses on the same day may have had overlapping buy lots.
2. The buys and loss arrays got out of sync and lots were split.

This is an alternative approach that repeatedly picks the (singular) earliest loss and finds lots to cover it.
The change is pretty invasive, so I don't necessarily expect you to merge as-is, but I do think it fixes some legitimate deep rooted issues, so I don't want it to get lost.