maint: ignore unsaved emacs files

maint: ignore unsaved emacs files

I did a 'git add .', then realized that it ended up trying to
add the emacs lock file for a corresponding file that I had not
yet saved all my edits; thankfully I noticed it in time.  Since
we already exclude other temporary files, this makes the most
sense for preventing such a mistake from actually hitting upstream.

* .gitignore: Add .#* to the exclude list.