When jumping to OUnit logs, make sure it is possible to jump back to normal file

[gildor478]

This bug has been migrated from artifact #1630 on forge.ocamlcore.org. It was assigned to user100.

user102 posted on 2016-07-17 13:09:16:

I often found myself have to re-open an OCaml source file, because there is no way to jump back from a log file.

This happens because the detection of original source file is broken.