Have you tried "apt-get update" or "aptitude update" before trying to
install these packages?
Yes, I did "aptitude safe-upgrade" after "aptitude update" and then "aptitude full-upgrade".
I selected "n" and it prompted me to "downgrade the packages to testing". This means that the versions it had were newer than testing, i.e., from sid. How could this be if I followed 2.7.3 of DR? According to that, my candidate version is appropriately set:
stuckey@debian:~$ cat /etc/apt/apt.conf
APT::Default-Release "testing";