`.pytxcode` needs to be more robust

[gpoore]

In some cases, code can be written to the .pytxcode after the settings have been written. This causes errors, because parsing assumes that settings are last. The new, upcoming format for .pytxcode should allow content in an arbitrary order, unless the order can absolutely be guaranteed (which is unlikely).

Example case here. In this case, and similar cases seen in the past, a \clearpage was sufficient. But in principle there might be a way to break that under some conditions.