Merge gsoc2012-doxygen branch

I'd like to merge this branch into master. There is still a lot of work to do here (and I intend to fix at least some bugs), but this seems to be already useful in its current state, i.e. it's better than nothing and doesn't seem to break anything not related to Doxygen (although this remains to be tested, which is another reason for creating this pull request: I hope Travis will do it for me).
This new function doesn't appear to ever be defined or used (and we already have `Swig_warning()).