Dev: backing out a stable release is difficult

[rmackay9]

When backing out a stable release, the procedure (pre-4.2.x) has been to simply:

• delete and re-create the ArduCopter-stable and ArduCopter-stable-heli tags to point at the previous release
• add a commit to master to trigger the build
• warn the users on discuss and facebook

Sadly during the backout of 4.2.2 this happened:

• The majority of boards shifted back to 4.2.1 (good!)
• MP's display remained at 4.2.2 and it also continued to pop-up notifications to users saying that a new release was available (when it was not)

The issue appears to be that in the manifest some stable builds were still appearing as 4.2.2 (I don't know why) and MP always displays the highest version number available.

FYI @peterbarker @meee1

[meee1]

Mission planner uses this
there is a prefilter on this to get just the release type
where reltype = OFFICIAL
options = Manifest.Firmware.Where(a => a.MavFirmwareVersionType == reltype.ToString());

// get max version for each mavtype
options = options.GroupBy(b => b.MavType).Select(a =>
a.Where(b => a.Key == b.MavType && b.MavFirmwareVersion == a.Max(c => c.MavFirmwareVersion))
.FirstOrDefault()).ToList();

and is grabbing
https://firmware.ardupilot.org/manifest.json.gz