No constructor proxies for IO, Error.

[som-snytt]

Is this a good time to relax the restriction on constructor proxies?

Perhaps, as a compromise, the restriction applies if there is an existing apply that is shadowed.

5 |val out: IO^ = IO()
  |               ^^
  |               Reference to constructor proxy for class IO
  |               shadows outer reference to object IO in package java.lang
  |
  |               The instance needs to be created with an explicit `new`.