MANUALDEPWAIT builds should migrate to SUPERSEDED as NEEDSBUILD does

[William Grant]

See https://edge.launchpad.net/ubuntu/+source/mplayer/2:1.0~rc2-0ubuntu1 for an example of bad behaviour. Those depwait builds are going to stick around for a while, as some of those archs will probably never have the dependency build for them. They should be superseded, like needsbuild is.

[Celso Providelo (cprov)]

I will confirm it as a wishlist because it's not like we a doing anything wrong, instead we are not being clever enough.
Hopefully when we implement build creation during upload time we can also mark unstable (pending & depwait) build records for previous versions as SUPERSEDED.