Correct comment for 15-of-15 p2sh script size

The original comment forgets to account for the script push which will
need an OP_PUSHDATA2 + 2-bytes for the 513 script bytes.

props davecgh
fixes #4224

src/main.cpp

@@ -488,7 +488,7 @@ bool IsStandardTx(const CTransaction& tx, string& reason)
     // Treat non-final transactions as non-standard to prevent a specific type
     // of double-spend attack, as well as DoS attacks. (if the transaction
     // can't be mined, the attacker isn't expending resources broadcasting it)
-    // Basically we don't want to propagate transactions that can't included in
+    // Basically we don't want to propagate transactions that can't be included in
     // the next block.
     //
     // However, IsFinalTx() is confusing... Without arguments, it uses
@@ -521,7 +521,7 @@ bool IsStandardTx(const CTransaction& tx, string& reason)
     {
         // Biggest 'standard' txin is a 15-of-15 P2SH multisig with compressed
         // keys. (remember the 520 byte limit on redeemScript size) That works
-        // out to a (15*(33+1))+3=513 byte redeemScript, 513+1+15*(73+1)=1624
+        // out to a (15*(33+1))+3=513 byte redeemScript, 513+1+15*(73+1)+3=1627
         // bytes of scriptSig, which we round off to 1650 bytes for some minor
         // future-proofing. That's also enough to spend a 20-of-20
         // CHECKMULTISIG scriptPubKey, though such a scriptPubKey is not