blockchain: during fastAdd or if block wasn't already valid, mark as valid in index
blockchain: during fastAdd or if block wasn't already valid, mark as valid in index

tb00/btcd,davecgh/btcd,ppcsuite/ppcd,dajohi/btcd,btcsuite/btcd,wallclockbuilder/btcd,ltcsuite/ltcd,btcsuite/btcd,tb00/btcd,davecgh/btcd,dajohi/btcd,ltcsuite/ltcd,dajohi/btcd,wallclockbuilder/btcd,ppcsuite/ppcd