[pkg] fix debian packaging (closes #3058542) - remove useless Python 2.4 reference, - simplify dh_install configuration to install files consistently instead of having half in /usr/lib/pythonXX and half in /usr/share/pyshared, - incidentally, this makes the package work on squeeze. Regression from eaa58d1c7d5f

etc/init.d
etc/cubicweb.d
etc/bash_completion.d
usr/bin
usr/share/doc/cubicweb-ctl
var/log/cubicweb
var/lib/cubicweb/backup
var/lib/cubicweb/instances