Various minor fixes and compiler warnings
This MR fixes a few lingering issues before release of 5.0b:
- Various compiler warnings and CMake warnings for policy issues on newer CMake versions.
- Remove a bunch of old XML files and an automake file (!)
- Add a
.gitattributes
that makesgit archive
more sane, and enables union merge forCHANGELOG.md
. - Fixes for macOS tests where
SessionReader
constructor throws a segfault if no arguments are passed.