diffsum.icn: Program to count lines affected by a diff

Usage:  diffsum [file]

Diffsum reads a file containing output from a run of the Unix "diff"
utility.  Diffsum handles either normal diffs or context diffs.  For
each pair of files compared, diffsum reports two numbers:
     1. the number of lines added or changed
     2. the net change in file size
The first of these indicates the magnitude of the changes and the
second the net effect on file size.