Solve the following problems:
* mishandling of commit message lines similar to committer lines
* UnicodeDecodeError with commit messages that cannot be interpreted
as utf-8
I replaced git-set-file-times with an improved version that I wrote
recently (in python3). A new script uses it to figure out the
last-modified year for each *.[ch] file and updates its copyright.
It also puts the latest year into the latest-year.h file for the
output of --version.
