Capability-matching generic code should not be accepted

[jasoncarr0]

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his example code is accepted by the compiler, but should not be:

class Worse[T]
  new create(out: OutStream, x: (String | T)) =>
    match x
    | let s: String val => out.print(s)
    else
      out.print("If x was a String you bet the compiler acted weirdly")
    end

actor Main
  new create(env: Env) =>
    let s1: String ref = String
    Worse[String ref](env.out, s1)
    s1.append("Ohno")

Currently, this compiles, and results in running the else branch of the match. It should not compile at all, as the accurate dynamic semantics of this would result in a successful match against String (without regards to capabilities) and hence it should be rejected as a capability-only match.