Use Exif.OlympusEq.LensType and give it precedence over
Exif.OlympusEq.LensModel and Exif.Photo.LensModel since it is normally
the most precise data and the string used in (the current svn of)
lensfun.
Merge branch 'olympus-ft-lens-recognition' of https://github.com/fingerle/darktable