Assertion failure in VCL_DelBackend()

[Dridi Boukelmoune]

>> A backend when popens a CGI command for this request ?
>
> I'm sure I wouldn't do that by creating and then destroying a struct
> director every time. Of course the API can be open for unforeseen
> ideas, but in this case it seems like a real stretch.

Agreed, deleting a struct director carelessly could lead to dangling
pointers in other transactions.

Maybe I should document a rule of thumb such as never deleting a
struct director that is made available to VCL code. If you delete the
director/backend underneath it's fine. You can simply get a NULL
director from the resolve function.

> And as I said earlier, I have no intuition at all about what a
> PRIV_CALL-scoped backend could be.