Some tiny bugfixes:

* Don't let ledger idle interval get too short
* Fix CBigNum::setuint256
* Fix SqliteStatement::isError
* Remove dead code, fix incorrect comments
* Check for NULL earlier in CKey constructors
* Prevent expire times from underflowing in TaggedCache

src/ripple_app/data/SqliteDatabase.cpp

@@ -471,10 +471,10 @@ bool SqliteStatement::isError (int j)
     case SQLITE_OK:
     case SQLITE_ROW:
     case SQLITE_DONE:
-        return true;
+        return false;
 
     default:
-        return false;
+        return true;
     }
 }