Do not let make_dir fail on EISDIR

Some systems set errno to EISDIR when a directory exists already,
instead of EEXIST.
Update help output shown by "minidlna -h".

Reported-by: (and original version by) Benoît Knecht <benoit.knecht@fsfe.org>
Fix deprecation warning about AM_INIT_AUTOMAKE.
Set the conversion indicator on fake resources for Sony BDP's.  New models support most of these natively, and don't like fake resources.