Fix broken stacktrace navigation to references of the form `foo/eval16959/fn`

I closed #850 prematurely and cannot reopen it now. The problem is not fixed. Sometimes info middleware doesn't return file location. In those cases just pick the file from stacktrace.

>>> Bozhidar Batsov on Fri, 17 Oct 2014 12:27:49 -0700 wrote:

> The middleware error should also be visible in the REPL buffer, so users are
> unlikely to miss it.

I was missing it till I started investigating what was going on. My repl
is full of my own user errors so I am completely ignoring it.