audiocd: reset read speed to maximum for extraction

cdparanoiasrc doesn't do this itself (though it should), so do it
ourselves.  setting read-speed to -1 means cdparanoiasrc won't apply
it to the device, so use 0xffff instead, which is the maximum value
for the scsi command that gets sent to the device.
Updated Serbian translation
Updated Slovenian translation
podcast: add podcast search infrastructure

This searches iTunes and Miroguide for podcast feeds.  Not hooked
up to any UI yet, but will be soon.

This also makes json-glib a required dependency, which means the
last.fm plugin can always be built.
podcast: add entry type for podcast search results

This will be used to represent episodes in podcasts in search results.
Entries of this type are not saved to disk, and don't do tricky things
with mount points vs locations, but otherwise they're like episode entries.
podcast: new podcast subscription dialog

This uses the previously added podcast searches to find podcasts,
previews podcasts before subscription (including playback of episodes)
and makes importing feeds via OPML a bit easier too.
metadata: install ext-db headers (bug #676860)
Updated Polish translation
podcast: move info bar for errors to the top of the dialog

also fix the parent class for the dialog to be GtkBox rather than
GtkVBox and/or GtkHBox.
Updated Spanish translation
Updated Spanish translation
Updated Slovenian translation
Updated Latvian language
Updated Indonesian translation
Updated Hungarian translation
Updated Lithuanian translation
Updated Czech translation
Updated British English translation
Updated Spanish translation
[l10n] Update Japanese translation