add missing header end comments

- ensures a consistent usage in header files
- also add a blank line after the copyright header where missing
- also remove orphan new-lines at the end of some files
Merge pull request #4779

093303a add missing header end comments (Philip Kaufmann)
Create build-aux/m4 dir. Move m4 scripts for out-of-src builds.
Remove pkg.m4. Update .gitignore.