Merged.

Looks good to merge!

Here are the experiment results:

http://ai.cs.unibas.ch/_tmp_files/seipp/issue803-v1-issue803-base-issue803-v1-compare.html

Code looks good.

I made a pull request at https://bitbucket.org/jendrikseipp/downward/pull-requests/95 .

I'll set up experiments later.

Planning with the debug64 build currently leads to an assertion failing:

src/search/algorithms/int_hash_set.h:210: std::pair<int, bool>
int_hash_set::IntHashSet<Hasher,
Equal>::insert(int_hash_set::IntHashSet<Hasher, Equal>::KeyType,
int_hash_set::IntHashSet<Hasher, Equal>::HashType) [with Hasher =
StateRegistry::StateIDSemanticHash; Equal =
StateRegistry::StateIDSemanticEqual; int_hash_set::IntHashSet<Hasher,
Equal>::KeyType = int; int_hash_set::IntHashSet<Hasher, Equal>::HashType
= unsigned int]: Assertion `hasher(key) == hash' failed.

Changing the line in question to "assert(static_cast<HashType>(hasher(key)) == 
hash);" solves the problem, but we'd also like to add more checks ensuring that 
we use the correct data types.