various typos

src/main.cpp

@@ -1191,7 +1191,7 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState& state, const C
                 // nSequence >= maxint-1 on all inputs.
                 //
                 // maxint-1 is picked to still allow use of nLockTime by
-                // non-replacable transactions. All inputs rather than just one
+                // non-replaceable transactions. All inputs rather than just one
                 // is for the sake of multi-party protocols, where we don't
                 // want a single party to be able to disable replacement.
                 //
@@ -2042,9 +2042,12 @@ 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 optimization 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;
@@ -4881,7 +4884,7 @@ void static ProcessGetData(CNode* pfrom, const Consensus::Params& consensusParam
                     {
                         // If a peer is asking for old blocks, we're almost guaranteed
                         // they wont have a useful mempool to match against a compact block,
-                        // and we dont feel like constructing the object for them, so
+                        // and we don't feel like constructing the object for them, so
                         // instead we respond with the full, non-compact block.
                         if (mi->second->nHeight >= chainActive.Height() - 10) {
                             CBlockHeaderAndShortTxIDs cmpctblock(block);