swift234

implement <rdar://problem/16310561> Property vtables not set up correctly

This switches property/subscript dispatch to use virtual dispatch instead of static
dispatch.  This currently only works for computed properties (and subscripts of 
course), not stored ones yet.

Long story short, this:

class Base {
  subscript() -> Int {
    return 42
  }
}

class Derived : Base {
  @override
  subscript() -> Int {
    return 9
  }
}

var a : Base = Derived()
print(a[])

now prints 9 instead of 42.



Swift SVN r15142