bug#24073: 24.5; outline-on-heading-p sees any invisible text property as outline invisible

[Paul Rankin]

Noam Postavsky <npostavs@users.sourceforge.net> on Thu, 28 Jul 2016 22:07 -0400:
> I think it's because outline-invisible-p is a defsubst, so when
> compiled, callers don't actually reference the symbol
> `outline-invisible-p' at all.

Ah yes. Thanks. A predicate function that doesn't return a t or nil and misuses 
defsubst! For shame outline... for shame....

Is there any way for a package to work around this with outline in its present 
state?