Restore the compilation of linalg by tweaking the complex disambiguation rules

This commit is a potentially breaking change, but the problem was that
linalg was relying on a previous bug in the compiler, which was fixed
in the concepts branch.

With the old disambiguation rules, generic procs like:

proc \`==\`[T](lhs, rhs: T)

and

proc \`==\`(lhs, rhs: Matrix32|Matrix64)

.. were considered equal, even though it's obvious that the second one
should be preferred. We never noticed this, because there was a bug in
sigmatch incorrectly counting one of the params of the second proc as
a non-generic match, thus giving it an edge.

This commit gives some preference to tyOr and tyAnd during the complex
disambiguation, which may affect overload resolution in other cases.

I see this only as a temporary solution. With my upcoming work on
concept refinement, I plan to provide an experimental implementation
of alaternative C++-like rules for determining which proc is more specific.
We can then discuss our strategy for dealing with such a breaking change.

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