When g_option_context_parse fails, context and error variables are not getting free'd
which results in memory leaks. Free'ing the same.
And replacing g_error_free with g_clear_error, which checks if the error being passed
is not NULL and sets the variable to NULL on free'ing.
https://bugzilla.gnome.org/show_bug.cgi?id=753852
Add (uninstalled) tool to create licenses-table.dat from liblicense's
RDF files. It's not very pretty and makes loats of assumptions about
the input, but should work. If things change, we can fix it then.
https://bugzilla.gnome.org/show_bug.cgi?id=646868