cleanup of IDownloadsObserver

this commit won't cleanly merge i guess...

please don't directly merge it, better do:

git remote add spring git://github.com/spring/pr-downloader.git
git fetch spring

WARNING: this will set your local branch to the same as spring/master (and remove all your commits):

git reset --hard spring/master

do the same for your remote branch:
git push -f

i hope thats ok for you / sorry for stealing kudos :-| but your commits were very "unclean" and thats really important to review changes and see bugs.