Updating std::hast<EntityId_t> to get a better unordered containers distribution [6895] #872
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Internally STL implementation of hash tables (unordered_map and set) use modulus operation to choose in which bucket put each element. Using an uniform distributed hash guarantees that the buckets get evenly filled and access time is minimum.
Until now we were using the whole EntityId_t interpret as a number as hash. That led to a non-uniform, unsuitable distribution because within each EntityId_t are kept flags not merely a counter. Now, only the counter value is used solving the speed issue.
This pull request contents has already been updated on 1.9.x (see #868).