Fix print0 position and backslash, set pipefail, allow overriding variables

First, a backslash was missing, causing /usr/share/tuxis-cron/cronscripts/prune-dir.cron: line 38: -ctime: command not found.

Second, -print0 is executed when the conditions preceding it match. It was placed after the -type condition, and before the -ctime condition, meaning all files in the given directory are deleted.

Third, due to the missing 'pipefail' option, issues with the find command were not reported.

Fourth, it was not possible to override variables (including ESCALATE_MAILTO). The local config file is now sourced.