Issue #954: Add support for Exif.CanonFi.FocusDistanceUpper and Exif.CanonFi.FocusDistanceLower. Thanks goes to Roman Lebedev for the patch.

git-svn-id: svn://dev.exiv2.org/svn@3254 b7c8b350-86e7-0310-a4b4-de8f6a8f16a3