assigning Medium package in replaceable class fails

[Michael Wetter]

Translating various models fail with the message

Buildings.Fluid.Boilers.Examples.BoilerPolynomial: 28:3-39:70]: component boi1 contains the definition of a partial class Medium.
Please redeclare it to any package compatible with Modelica.Media.Interfaces.PartialMedium.

or similarly

[5] 21:45:22 Translation Error
[Buildings.Examples.Tutorial.Boiler.System3: 153:3-160:72]: component boi contains the definition of a partial class Medium.
Please redeclare it to any package compatible with Modelica.Media.Interfaces.PartialMedium.

The problematic code seems to be in Buildings.Fluid.Interfaces.TwoPortHeatMassExchanger:

 replaceable Buildings.Fluid.MixingVolumes.MixingVolume vol
  constrainedby Buildings.Fluid.MixingVolumes.BaseClasses.PartialMixingVolume(
    redeclare final package Medium = Medium,
    ...

This is a blocker if users want to use OpenModelica during the tutorial at the MODPROD workshop.