filters: Make in-list() more portable

Instead of using getline(), use fgets() which is more widely available.
The downside of this is that lines are now limited to 16k chars in
length.

This fixes #213.

Reported-by: Michael Hocke <michael.hocke@nyu.edu>
Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>