revive error grouping?

_From [derek.br...@gmail.com](https://code.google.com/u/117968039472581148324/) on December 10, 2010 17:58:08_

PR 486051

When looking at 100k errors in an app, even groups and duplicates didn't
help much as there just too many of them. Also, some groups had too many
errors in them. There was no easy way to tell how many unique errors were
in each group and how much of the total each group constituted. So with
each group, number of unique errors and total number of errors should be
printed. While at it should we print the percentage of total errors a
group constitutes?

_Original issue: http://code.google.com/p/drmemory/issues/detail?id=160_