PR #4502 is now in devel

[Edward K. Ream]

PR #4502 adds efc.GitDiffController(c).summary_diff_two_revs. This script helper provides "summary" diffs of files:

- Omits cruft such as changes to Leo's sentinel comments.

- Separates the components of the diffs.

I find it significantly easier to understand than, say, efc.GitDiffController(c).diff_two_revs.

The PR shows how to diff all the files in PR #4487, the summary of all changes made in Leo 6.8.8. I merged this PR immediately because I need it for the next phase of my work. I plan to undo (using #fmt: skip comments) some of the recent formatting changes.

This PR only adds code, so it should be completely safe. Onward!

Edward