The progress bar will now travel from 0 to 20% during pass 1, from 20%
to 95% during pass 2, and from 95% to 100% during passes 3, 4, and 5.
Previously, the progress bar was not displayed at all during pass 1,
slowly traveled from 0 to about 50% during pass 2, and then very rapidly
traveled from 50% to 100% during passes 3, 4, and 5.
Note that fsck_ffs is the only user of fsck/progress.{c,h}.