bip-0300: Forbid extraneous OP_DRIVECHAIN outputs in M5/M6

Author: luke-jr

bip-0300.mediawiki

@@ -398,7 +398,7 @@ Every time a deposit/withdrawal is made, the old CTIP is spent and a new one is
 
 Every M5 is valid, as long as:
 
-* It has at least one OP_DRIVECHAIN output -- this becomes the new CTIP.
+* It has exactly one OP_DRIVECHAIN output -- this becomes the new CTIP.
 * The new CTIP has '''more''' coins in it, than before.
 
 
@@ -412,6 +412,7 @@ M6 is invalid if:
 * The first output of M6 is NOT an OP_DRIVECHAIN. (This OP_DRIVECHAIN becomes the new CTIP. In other words: all non-withdrawn coins are paid back to the sidechain.)
 * The second output is NOT an OP_RETURN script of exactly 10 bytes, of which 8 bytes are a serialized Bitcoin amount.
 * The txn fee of M6 is NOT exactly equal to the amount of the previous bullet point.
+* There are additional OP_DRIVECHAIN outputs after the first one.
 
 Else, M6 is valid.