function-exists() and mixin-exists() return false for local definitions

[nex3]

Both function-exists() and mixin-exists() should return true for functions or mixins (respectively) defined in local scopes, as so:

.scope {
  @function local-function() {@return null}
  @debug function-exists(local-function);

  @mixin local-mixin() {}
  @debug mixin-exists(local-mixin);
}

Both of these @debugs should print true, but they currently print false.