If 'apt-ftparchive packages /path/to/files/' (or sources) is used the
files to include in the generated index (on stdout) were included in the
order in which they were discovered, which isn't a very stable order
which could lead to indexes changing without actually changing content
causing needless changes in the repository changing hashsums, pdiffs,
rsyncs, downloads, ….
This does not effect apt-ftparchive calls which already have an order
defined via a filelist (like generate) which will still print in the
order given by the filelist.
Note that a similar effect can be achieved by post-processing index
files with apt-sortpkgs.
Thanks: Chris Lamb for initial patch & Stefan Lippers-Hollmann for testing