Don't use atd if /sbin/shutdown is systemd
Fix tar command in Makefile

Also, move README to README.md and get rid of the symlink. The symlink
will not be transformed properly by the "make dist" tar command.
Update README for RHEL/CentOS/Debian 7
Import tingle.spec fixes from downstream
Bump to 0.5.3
Add a few more .PHONY Makefile targets

We allow the tarball to be rebuilt even if no sources have changed.
Order PATH correctly
Ensure TINGLE_PREFIX works properly on /etc/ files
Only use killswitch on dangerous actions
Fix numerous questionable shell constructs
Don't give up if the readlink fails
Do not create /etc/nologin -- some distros don't remove it
Fix dependencies in Debian package
Bump to 0.5.4