Previously, I used a shell script to extract modification date ranges
from the Git history, but that was complicated and unreliable, so now
every file just gets the same year range in its copyright header. If
someone needs to know when a specific file was modified and by whom,
they can look at the Git history themselves; no need to include it
redundantly in the header.
The previous code caused frequent seed collisions for successive calls
to the no-arg constructor, even for single threaded workloads. This
patch should avoid such collisions in both single and multi-threaded
cases.
