[Patch]: RT51679: toke_scan_str doesn't handle errors, returns garbage

Patch/tests/documentation for [RT51679](https://rt.cpan.org/Ticket/Display.html?id=51679). It targets the same function/test/POD section as [this](http://github.com/rafl/devel-declare/pull/2), so built, as a separate patch, on top of it.