download file urls are too long

following on from https://bugs.launchpad.net/pad.lv/+bug/788837

Launchpad file download URLs look like:
https://launchpad.net/linux-linaro/11.05/11.05-final/+download/linux-linaro-11.05-2.6.38.tar.bz2

there is generally a lot of redundant information here, if the project uses fully-qualified download filenames, as most do

It would be better if this was something like

https://launchpad.net/linux-linaro/+download/linux-linaro-11.05-2.6.38.tar.bz2

I don't know if they're currently constrained to unique names. If they're not, this could perhaps be a redirect that works only in the common case where the name is unique.