swift234

Further improve the error message when self escapes in a root class before
its fields are initialized.  Before:

   t.swift:18:24: error: variable 'self.B' captured by a closure before being initialized

after:

t.swift:19:24: error: 'self' captured by a closure before all members were initialized
    self.A.withCString {  cString -> () in
                       ^
t.swift:14:7: note: 'self.B' not initialized
  var B: Int
      ^

This drives home the fact that 'self' is being captured here, not the individual
properties.