Spec needs to specify that the state used in eth_call is AFTER execution of the block

Everywhere where the API takes `block_number` like` eth_call `, the spec needs to specify that
the state used for execution is the state AFTER execution of the block with the specified` block_number`.

Currently the spec does not not mention whether the state is BEFORE or AFTER.

This creates ambiguity and implementation errors, since some people err to the side of the state BEFORE block execution.