Fix a copyright year update problem in gdb/gnulib

[Joel Brobecker]

While looking at another change, I noticed that the year range
for copyright.py was still ending with 2012, instead of 2013.
I think this is related to the move of the gnulib actual import
to a subdirectory of gnulib - we just forgot to update the
copyright.py script to include the files we created after that
move.

This patch series fixes the script first, and then brings the changes
which should have been part of the update earlier this year...