IGenerationHandler story: bring IncrementalGenerationTest back to life (though only 2 of 4 pass now).
IGenerationHandler story: drop uses of estimateCompilationMillis, correctly group models by module, use number of models as progress fraction
ReloadableSModelBase: datasource tracking extracted into separate facility to split editable and reloadable model (now EditableSModelBase extend ReloadableSModel, implies any model we can modify(promise of EditableSModel) tracks its datasource and reloads, which is not true for in-memory/constructed models); EditableSModel API duplicates/exposes certain aspects of ReloadableSModelBase, likely erroneously.
Canonical path for temp location to cope with test failures, where files written though canonical fs location are not visible through an alias.