Use secondary URLs to install and update packages #20
Description
secpkg install and secpkg update should use additional URLs specified in .secpkg files to query which one announces the most current head (as given by the highest last signed hash chain number).
The one with the highest number is tried first and the download URL it announces are tried to download the update, if necessary. If all URLs for a DNS entry fail the next DNS entry is tried.
Download URLs are only used in combination with the DNS head on the domain that announces them.