Better accommodation for Xscreensaver users

[linkp]

Every time bunsen-utilities updates, it clobbers my edited bl-lock script and breaks my xscreensaver lock. This patch fixes that without breaking the expected behavior for those using light-lock.

I incorporated a variant of the testing logic used in debian/bunsen-utilities.postinst in the bl-lock script to make it use 'xscreensaver-command --lock' as the LOCK_COMMAND if xscreensaver is installed and light-locker is absent. It will default to light-locker in all other conditions.

I updated the test and warning in debian/bunsen-utilities.postinst to only display the warning if xscreensaver and light-locker are both installed, as the presence of xscreensaver alone is properly handled by this update to bl-lock.

[johnraff]

Hello @linkp and thank you for your contribution. The dev team have given some thought to your suggestion, but have decided at this time not to patch the bl-lock code.

It is quite easy for a user who wants to customize /usr/bin/bl-lock to copy the file to their ~/bin directory and edit it there. As long as /home//bin is in their $PATH (in BunsenLabs it is by default) then their local copy will take precedence over the system file.

(In fact any system file installed by a Debian package will be overwritten by package upgrades, and some local solution is always recommended, except for conffiles under /etc.)

Thanks again for taking the time to point out this potential issue, and sharing a solution.