Add a framework for detecting databases that need updating.

Put transaction from account_tx command in transaction application sequence.
CAUTION: This modifies your databases and will cause a delay on your next startup.

src/cpp/ripple/LedgerMaster.cpp

@@ -106,7 +106,7 @@ Ledger::pointer LedgerMaster::closeLedger(bool recover)
 					++recovers;
 			}
 			catch (...)
-			{
+			{ // CHECKME: We got a few of these
 				cLog(lsWARNING) << "Held transaction throws";
 			}
 		}