container/mts/psi: write function that returns a standard PSI rather than globals

[Saxon Milton]

Instead of having global ‘standard’ PAT and PMT which has recently been discovered to be a stupid idea, we could have a function to return a basic PAT and PMT.

[Alan Noble]

Plus the constructor function could have params for specific data, etc.

[Saxon Milton]

Yes true

[Saxon Milton]

Resolved in PR #409