Bug#56568: apt-get hangs trying to remove half installed package
The dselect method of apt hung for >20 mins when trying to remove a
half installed version of emacs. I eventually gave up waiting.
dpkg --remove emacs didn't work either, but suggested I install emacs
and then remove it (which worked).
I got into this state by aborting an upgrade half way through when I
was worried my disk would fill up. This resulted in one of the emacs
packages being stopped half way through an install/upgrade.
Sorry to be a bit vague, but I did this last week and can't remember
all the nitty gritty details.