Config_error does not support adding additional context

[jbigot]

Very often, the context for a configuration error can only be provided higher in the call stack. In this case, one would like to add information to the Config_error exception.
For example:

try {
} catch (Config_error& err) {
    throw Config_error{/**/, "Some more info"};
}

Unfortunately, the current implementation doesn't make it possible to extract the line & column of the error from the exception so this is not possible.

[benoitmartin88]

update deisa plugin when this issue is fixed.