Un-XFAIL, and just comment out and add a FIXME to the two cases that fail on
linux.
Closes#577. This still doesn't compare <, >, etc for channels, ports and
tasks, but since they use pointer equality, that's a bit difficult to set up.
While it is still technically possible to test stage 0, it is not part of any
of the main testing rules and maintaining xfail-stage0 is a chore. Nobody
should worry about how tests fare in stage0.
Includes assignment operations. Add regression tests for lots of less useful,
less used or unexpected combinations, as well as a selection of compile-fail
tests. Closes#500 (again!)