Makefile.am: verify the dist packages build
add test/test_rdnss.conf to DIST_EXTRA
Update CHANGES and configure.ac for v2.4
Makefile.am: add more package checks

..I've been forgetting to tag, push and test the packages, so this
change will do those checks for me when I make packages.
Merge branch 'packaging_helpers'
Makefile.am: packaging helper tweaks

Don't check for tag until after the packages is built and checked.