message: Improve CheckInputs() comment about sig verification
diff: @@ -1908,9 +1908,12 @@ bool CheckInputs(const CTransaction& tx, CValidationState &state, const CCoinsVi
  // Only if ALL inputs pass do we perform expensive ECDSA signature checks.
  // Helps prevent CPU exhaustion attacks.
  - // Skip ECDSA signature verification when connecting blocks
  - // before the last block chain checkpoint. This is safe because block merkle hashes are
  - // still computed and checked, and any change will be caught at the next checkpoint.
  + // Skip ECDSA signature verification when connecting blocks before the
  + // last block chain checkpoint. Assuming the checkpoints are valid this
  + // is safe because block merkle hashes are still computed and checked,
  + // and any change will be caught at the next checkpoint. Of course, if
  + // the checkpoint is for a chain that's invalid due to false scriptSigs
  + // this optimisation would allow an invalid chain to be accepted.
  if (fScriptChecks) {
  for (unsigned int i = 0; i < tx.vin.size(); i++) {
  const COutPoint &prevout = tx.vin[i].prevout;
  