Network changes no longer leave old connections behind, and other improvements

Fixes

• Changing network settings on the player no longer leaves the old connection behind. On a player set up over ethernet more than once, a new one piled up with every change.

Improvements

• The latest disk image has a download address that stays the same from release to release, so a bookmark or a build script doesn’t need updating every time we ship. The current address is in the guide to writing the image.
• Dependencies and system libraries updated.