New script: update-trackers.sh

Updates the reference branch in the bug trackers specified on
command-line to the latest (or specified) commit (i.e. pull from
upstream), then rebases the branch bearing the same name as the repo on
top of the target commit (by default the HEAD of the reference branch).
Set executable mode for update-trackers.sh
Improve check_lineterm.php

Remove code duplication; ignore '.git' directory and remove CVS
reference; improve output.