Current separation of part of the logic into include_path
obscures the purpose of Dirs (see expand_file_names).
Moreover for each particular Erl its source file was included
twice in Dirs, which is now corrected.
Also InclDirs (specified in erl_opts) as part of erlcinfo
since they can affect resulting graph, which needs to be
therefore regenerated when InclDirs change. See added
test as an example.
