Minimum version for doxygen

[Chris Richardson]

I just had a failed compile because an old version of doxygen created a useless docstrings.i file. We need to have a version check in CMakeLists.txt

[Tormod Landet]

How old? I already have a workaround for version doxygen 1.8.13 which has a large regression (segfaults while parsing the dolfin code). See issue #849. If we knew the minimum required version it would be very easy to do something similar for versions older than that

[Chris Richardson]

Yes, it is tricky, given that some of the latest versions are not working either. I just had a couple of systems with 1.5 and 1.6 editions of doxygen, which caused major meltdowns. Maybe we can have a whitelist of known working versions, and later?

[Tormod Landet]

Yes, I already compiled quite some versions of doxygen to test, so I can probably compile some more to see which versions work