Code review comment for lp://staging/~michihenning/unity-scopes-api/qt-coverage

To clarify - this fails to regenerate symbols for me in my canned-query-data branch, based on this branch.

> Michi, I've no luck running the updated diff_script, it's failing to do the
> job in different ways:
>
> 4006 + with open('/tmp/symbols.diff', 'a') as outfile:
>
> this change seems to be problematic, I'm getting an error saying
> /tmp/symbols.diff doesn't exist on start. It proceeds if I create an empty
> file in tmp. But then it fails in later steps.
>
> The line #94 of the script which prints the exception needs to use
> .decode(...) on the line, e.g.
>
> "raise Exception('Cannot parse demangled line: ' + line.decode('utf8'))"
>
> otherwise it fails with error about str + bytes concatenation.
>
> After fixing that line, it fails with this:
>
> vivid@vivid:/src/unity-scopes-api/build-area/unity-scopes-api-0.6.15$ ./obj-
> x86_64-linux-gnu/tools/symbol_diff
> Traceback (most recent call last):
> File "./obj-x86_64-linux-gnu/tools/symbol_diff", line 113, in <module>
> run()
> File "./obj-x86_64-linux-gnu/tools/symbol_diff", line 110, in run
> compare_syms(old_file, new_file)
> File "./obj-x86_64-linux-gnu/tools/symbol_diff", line 94, in compare_syms
> raise Exception('Cannot parse demangled line: ' + line.decode('utf8'))
> Exception: Cannot parse demangled line: libunity-scopes.so.3 libunity-scopes3
> #MINVER#