start using GError

[michalfabik]

As suggested by @ernestask.

[ernestask]

Needs more context.

It’s for things like

libreport/src/lib/problem_report.c

Line 307 in 54c08be

static int

If one decided to also output the format file name when an error occurs, one would also need to start adding random parameters to the function. However, if we just took, say, a GError ** in each failable function, we format the output however we want from callers, since they usually have what is missing; one can propagate errors up the call stack to no end (well, not really).

[ernestask]

Created a branch locally, but haven’t had time to actually work on it.