Bug in template instantiation scoping code

[sccolbert]

The compiler generates bad code for this:

from enaml.widgets.api import *


template Foo():
    Field:
        placeholder = 'foo'

enamldef Main(Window):
    Container:
        Foo(): f:
            f.text = f.placeholder

The scope key for the outer closure scope is not correctly passed to compiler helper which binds the expression for f.placeholder.