Here is the updated patch.  I incorporated all the feedback and requested
changes.  I've also found some other nits on my own.

I also looked more carefully at the CVS code and discovered that it only
looks for lines beginning with "CVS:", i.e., it doesn't care about a
following blank.  It does this in order to deal with editor that strip
trailing whitespace.

Changes since the last patch:
- don't activate log-edit-done-strip-cvs-lines by default just yet
- supply missing arg 'interactive to called-interactively-p
- use (case-fold-search nil) instead of (search-upper-case nil)
- mention log-edit-done-strip-cvs-lines in etc/NEWS
- explain why log-edit-done-strip-cvs-lines only looks for "^CVS:"
- doc strings for the log-edit-done-strip-cvs-lines tests
- factor out common code in log-edit-done-strip-cvs-lines tests
- 2 more tests for exactly the same behaviour as CVS

I've just noticed that, e.g. the lines following 
the "hook :options" in the log-edit-done-hook
defcustom, use TAB for indentation while indent-tabs-mode is turned off in
the top-level .dir-locals.el.  Do you care for consistency with the old
code?  This affects only a very small number of lines.

Sorry for this all taking so long.  And thanks for the feedback and the
patience.

--chris