clarify Fact comparisons
Created by: ederag
Base comparisons on fact elements only (id is ignored now).
The or
introduced in 9dc0d96a was too much magic.
With this PR the reasoning about fact equalities is simplified.
id
equality has now to be checked explicitly.
This is obviously a breaking change with respect to v2.2.1 which introduced fact comparisons
(precisely 3837ddcc).