/usr/share/postgresql/9.1/extension/pre_prepare--0.4.sql is in postgresql-9.1-preprepare 0.5-1.
This file is owned by root:root, with mode 0o777.
It is a symlink to /usr/share/postgresql/9.1/extension/pre_prepare.sql
/usr/share/postgresql/9.1/extension/pre_prepare.sql