Removed infolist code.

We're not using it anymore.
Removed the messages.ItemInfo class.

This has been replaced with data.item.ItemInfo
Must faster fix_html_header()

I'm not sure why, but on some header strings, the old
fix_html_header() would take forever to do the regex match and
basically hang the system for that time.  I timed it and it took about
100 seconds during which Miro was unresponsive.  The new code should
be fast enough to not do that.
bz19859: Fixed error while playing command line arguments
bz19856: fixed playback from guide sidebar
bz19463: added archive.org to the default sources list.
Fixed logging.stacktrace.

This new version works properly with positional arguments.
bz19671: remove Check version from the linux menus.

We had code to do it, but it was buggy.  Removed the
remove_from_parent() method since it didn't work and was generating
warnings.
bz19443: Fix global download rates after resuming downloads

This covers the OSX part of comment #4.
bz19831: disable menu items when no downloads are selected
Don't display removed items in the library tabs
bz19823: fixed ItemTracker code for a corner case.

Here's what seems to be happening:

 - I would delete an item that was playing.
 - The backend would update the play_count variable and send an ItemsChanged
   to the frontend
 - Before that message got to the frontend, it would remove the item from the
   DB and send a second ItemsChanged
 - The frontend would call connection.commit() to try to see the changes for
   the first message, but this would move the transaction past the second
   change as well and now the item is deleted from the database, but
   ItemTracker wasn't prepared for that
 - OSX would ask for the row for the item and we would crash.

Added a test and a fix for this.  The fix isn't pretty, but I tihnk it should
do the job.  Added some code so that we would fails earlier in the process if
a similar error happens.