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.
- Standardized the format of the opening comment, including adding a
brief description of what's in the file for those that lacked it.
- Added some missing copyright lines.
- Some minor whitespace tweaks (in a few of the files).
