Implemented the update option.
This patch makes the update option work, by enriching the Enable.pm file so that it does the work. I've therefore deleted the Update.pm which isn't useful anymore, and implemented a switch to direct the "update" command to Enable.pm. Also, to achieve this, this package now depends on libswitch-perl.
Last, I added a new "update" test in autopkgtest, to make sure it works as intended, testing also the option --offlinedata and --mirror while doing it.
I hope you'll like it!
Cheers,
Thomas Goirand (zigo)