Fix type inferencing and syntax highlighting for indirect private field reference

[eric-milles]

Consider the following:

class C {
  private foo
  def getFoo() { foo }
}
class D extends C {  }

def obj = new D()
obj.foo = null
print(obj.foo)

The property "foo" is read-only. "obj.foo = null" should not infer as the provate field from C. This is confirmed by running the script:

ReadOnlyPropertyException: Cannot set readonly property: foo for class: D

[eric-milles]