Stop trying if build failed more than n times

I just noticed that a lot of resources gets wasted when a build fails due to missing dependencies - because the build will be tried over and over again.

Good example: the kubuntu-members PPA.
There were about 5 packages looping since November because a common dependency wasn't able to build, so the higher level dependencies were waiting and apparently occasionally trying to build. I also noticed this with some other PPA's (like the one from lydia-pintscher where the package kdenetwork-kde4 was also looping for quite some time).

In order to prevent this, I think a package which is on dependency-wait should be built 3 to 5 times tops and after that declared to fail building (one can always trigger a rebuild manually anyway).

Considering I just found about 7 packages looping while looking at the build queue for just some minutes this might decrease the average queue length a lot.

Thank you very much for taking this into consideration.