etcupdate diff fails to show any diffs when POSIXLY_CORRECT environment variable is set. Instead of showing a diff, etcupdate diff emits diff --help for each file that was altered locally. This happens due to misplacement of the second -L argument of diff command, it is treated by getopt_long as an error.
This proposal fixes this behavior simply moving the second -L argument into a proper place.
A new feature comes along with this fix: -l argument for a diff command alters the way it shows differences. Instead of printing full diff, it reports changed file the same way as added/removed files are reported.