* module/language/tree-il/primitives.scm (+, *, cons*): In the case of
just one argument (the identity case), expand to (values x) instead of
just x. Fixes values truncation in that case.
(values): Likewise remove (values x) -> x translation, as the compiler
will do it for us, and this fixes (values (values 1 2)).
* module/language/tree-il/compile-glil.scm (flatten-lambda-case): Handle
`values' in a push context here.
* test-suite/tests/tree-il.test ("values"): Add some tests.