Explain how we're going to fix getLedgerByHash

src/LedgerHistory.cpp

@@ -63,6 +63,11 @@ Ledger::pointer LedgerHistory::getLedgerByHash(const uint256& hash)
 #if 0
 //		FIXME: A ledger without SHA maps isn't very useful
 // 		This code will need to build them
+
+	// The fix is to audit all callers to this function and replace them with
+	// higher-level functions that ask more-specific questions that we can
+	// test against our database
+
 	ret = Ledger::loadByHash(hash);
 	if (!ret) return ret;
 	assert(ret->getHash() == hash);