Merged, thanks.

The buildbot still has an unrelated problem on the mac but otherwise looks happy.

I had a quick look, looks good to merge!

Great. Malte, are you fine with us reviewing this, or should I put this into the
review queue?

Perfect. I have no objections to merging this.

Enabling pipelines didn't start them in the existing commits. I tried triggering
them manually but that didn't finish in reasonable time (no output or log or
anything like that). Locally running ./misc/run-all-tests works fine, though.

Looks good to me :-)

Do you want to enable the pipelines for this repo to see if all standard configs 
still run?

Here is a pull request for the updated CMake files and removing the empty files:
https://bitbucket.org/FlorianPommerening/downward-issues/pull-requests/28

Jendrik, can you have a look?

Quoting Malte's comment on a different issue 
(https://bitbucket.org/jendrikseipp/downward/pull-requests/58/issue535/diff#comment-24255752): 

"That would work, but I think it would be nicer to change the behaviour to the following (not necessarily now):

    1. Only specify the basename (without .cc or .h).
    2. If .cc exists, add it. If .h exists, add it. If neither exists, complain. 

This would make the "magic" a bit more consistent (.h and .cc would be treated equally, and planner.cc wouldn't 
need a special case), and we also wouldn't need to change the Makefile when we decide to add or remove a *.cc 
file.

Also, and perhaps more importantly, there are currently many cases where we have a *.h file and don't need it. 
This is mainly true for plug-ins (in the Fast Downward sense), which usually only depend on other things, but 
nothing depends on them."