[isabelle-dev] Towards Poly/ML 5.7.1

[Makarius]

Isabelle/8176914dae84 provides a more recent Poly/ML test version, which
can be used for testing like this in $ISABELLE_HOME_USER/etc/settings:

init_component "$HOME/.isabelle/contrib/polyml-test-905dae2ebfda"


After a few days, I will make this (or a later snapshot) the standard
Poly/ML version for isabelle-dev.

In a couple of weeks, David Matthews will release Poly/ML 5.7.1
officially, so now is a good time to see if it works smoothly.


	Makarius