Implemented as two functions: diffstat, which yields lines of text,
formatted as a usual diffstat output, and diffstatdata, which is called
inside diffstat to do real performing and yield file names with
appropriate data (numbers of added and removed lines).
Non-GNU versions of the sed(1) utility (i.e. on Solaris or BSD)
may not support extended regexps (i.e. including \| branches),
or may need a special option to enable it (like -E instead of -e).
Expand the sed RE in tests/test-patchbomb to fix running this
test on FreeBSD and Solaris.
