Update copyright.py

Update copyright.py

copyright.py needed an addition for unordered_dense.h.

Then, when running it, I saw it complain about some .pyc files I had
in the source tree.  I don't know why I had these, but the script
should ignore them.

For this, Kévin suggested using "git ls-files" to determine which
files to update -- that should automatically exclude any random files
in the tree.  This version of the patch makes this change.

There were complaints about some sim/ppc files that were renamed.
Ignoring the entire directory seems simpler given the comment.

I also made a few more minor changes:

* Removed the 'CVS' exclusion, as this hasn't been relevant in years.

* Moved the 'copying.c' exclusion to EXCLUDE_LIST

* Changed the script to run from the top level (we could have it
  automatically find this if we really wanted).

After this lands, I plan to run it and check in the result.  The patch
may be too large (and certainly too uninteresting) to post, so if/when
this happens I will send a brief note to the list about it.

Approved-By: Simon Marchi <simon.marchi@efficios.com>