Replace references to issue numbers from our original bug tracker

[s3rvac]

Currently, there are many references to our original bug tracker. For example, inside the bugs directory, subdirectories are named by their issue number. We should give them more descriptive names.

In general, whenever an issue from our original bug tracker is referenced, we should replace this occurrence with its description.

[s3rvac]

Done by @PeterMatula in bcbab21.