support lexer directives in input files

[gasche]

In Batteries it would be helpful to have qtest recognize lexer directives in input files (it gives compilation errors in the right place for test that comes from preprocessed .mlv files).

[c-cube]

So, this makes #line foo and the likes parsed properly? Good idea, thanks. Would it also work for, say, cppo?

[gasche]

I updated the PR with a cppo test. It works just fine.

[c-cube]

Very nice, thanks. Would you want me to release quickly?

[gasche]

Do as is convenient for you for the release -- it will be a nice ergonomic improvement, but it's not blocking anything Batteries-wise.