Fix handling of appup instruction generation with Dbgi chunk
Fix handling of appup instruction generation with Dbgi chunk

The addition of the Dbgi chunk has apparently resulted in a situation
where Elixir modules always appear to have changed even though they have
not; this made it so that `:beam_lib.cmp_dirs` always returned all
modules in both directories as having been changed, even though they
hadn't, producing extraneous instructions in the appup.

This change ignores the 'Dbgi' chunk, only considering the files to be
different if any other chunk was modified.

bitwalker/distillery,bitwalker/distillery