v2.2: workaround Plex Media Server failings

The Daily Show and The Colbert Report are invisible to PMS unless they
are in a subdirectory all by themselves.  So, add a :subdir option to
defseries.

Automatic database upgrade required.  Schema version 9.

API additions (both documented):

make-transmission-remote-handler: new keywords :ssh-user & :ssh-identity
defseries: new keyword :subdir