Fix 'getAffectedAccount' -- logic was totally wrong.

You can't get this from the transaction because which accounts a transaction
affects depends on things like which offers it winds up taking. And you
can't build it with the metadata because you don't always build the metadata
locally -- consider fetching a ledger after a network split. The only
rational way to do this is to build the affected account vector from the
metadata.

src/cpp/ripple/SerializedTransaction.h

@@ -60,7 +60,7 @@ public:
 	uint32 getSequence() const		{ return getFieldU32(sfSequence); }
 	void setSequence(uint32 seq)	{ return setFieldU32(sfSequence, seq); }
 
-	std::vector<RippleAddress> getAffectedAccounts() const;
+	std::vector<RippleAddress> getMentionedAccounts() const;
 
 	uint256 getTransactionID() const;