Merged and pushed.

Please merge.

Florian had a look at the pull-request [1] and is fine with the changes. Can I 
merge this?

[1] https://bitbucket.org/jendrikseipp/downward/pull-request/19/issue461-rename-
global-classes/diff

I think we should leave the state registry system unaffected, at least for now.
It only interfaces with a small part of the code.

What about StateID and StateRegistry?

Would make sense. This would also mean resorting the relevant #includes.

I guess we also want to rename the filenames and include guards, right?

operator.h -> global_operator.h
state.h -> global_state.h

Given that our states are always states of the global task, I think I'm in
favour of the renaming. I only see part of where this whole task class journey
is going at the moment, though. I expect that at the end these classes will
converge again to some extent (with the global task not being particularly
special), but even then I think it's good to rename the current state class for
now so that it won't be mistaken for something it isn't (a generic state class
applicable to all kinds of tasks).

I'd say we wait with renaming the State class until we're sure we need it, but I 
could also do it now if you prefer. What do you think?

We also discussed the possible renaming State -> GlobalState.

At this point, I'm not sure if it is going to be necessary, but I think it's
more likely than not.

(As Gabi mentioned, I'd recommend doing this one with an IDE -- much less work.)

As discussed offline we need to rename some classes before we can merge issue439 
(task class). The proposed renamings are:

Operator -> GlobalOperator
Effect -> GlobalEffect
Condition -> GlobalCondition