[tests] Add tests to exercise various code paths in Select.replace() The original patch for bug #1190458 broke tests in CubicWeb. The patch has now been amended to fix the broken paths (namely, replacing the 'in' tests with appropriate 'is_equivalent' loops). These tests are adapted from CubicWeb's own test suite, especially those that test FTIRANK() on sqlite (the function exists but is replaced by a no-op).

TODO list for the rql package
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* retirer les restrictions e_type = [A-Z][a-z_]*
                           r_type = [a-z_]*

* detecter les erreurs ASAP pour éviter stcheck

* tests unitaires pour sqlgen

* revoir tutoriel

* specification 1.0