This channel_icons.pl script replaces all previous master iconmap handling by
using services.mythtv.org as the data lookup point.  It handles icon
downloading and database updates internally, and allows for matching on more 
precise fields like xmltvid instead of callsign, which is not often used 
outside of the US.

master_iconmap.xml is provided for legacy reasons (until support for these
features is added to MythTV itself), and new copies can be generated via:

  ./channel_icons.pl --iconmap > master_iconmap.xml