Part of issue509.

Fantastic! Merged and pushed.

Yes, please!

The experiments for this one are done and it looks like nothing changed beyond
the usual noise (if anything, there is a small positive trend in total time):

http://ai.cs.unibas.ch/_tmp_files/pommeren/issue792-v1-opt-issue792-base-issue792-v1-compare.html

Can I merge this?

Done with my comments. All my comments are about the comments.

I'm done with this round of review.

I updated the pull request with the changes from issue774 and issue824.

Thanks Jendrik. I removed the old forward declaration and updated the pull request.

I only left one minor comment on Bitbucket. Otherwise, the code looks good to me.

The following pull request is against issue774 because it is easier to merge it
before we consider this issue.

https://bitbucket.org/FlorianPommerening/downward-issues/pull-requests/46

While moving to the new task interface, we want to get rid of the global
successor generator. Instead of having one global object, it should be created
from a task proxy.