Can't access fields on varargs case class

[kenbot]

If a case class field is marked as varargs, then "get" and "set" expressions cannot recognise the expected copy method.

Once #3 is resolved, "get" shouldn't be a problem at least.

scala> case class Foo(ns: Int*)
defined class Foo

scala> get"$res1.ns"
<console>:26: error: Can't update 'ns', because no 'copy' method found on Foo
       get"$res1.ns"
       ^

scala> set"$res1.ns" := Nil
<console>:26: error: Can't update 'ns', because no 'copy' method found on Foo
       set"$res1.ns" := Nil
       ^

[kenbot]

A copy method actually doesn't get generated for varargs case classes. Our options are:

• Leave the (essentially accurate) error message as is
• Produce a custom error message explaining the situation with varargs case classes
• Put in a special case that can modify varargs case classes using the companion object or constructor, rather than copy.

[kenbot]

It can wait until after 1.0.