HFS Plus (Mac OS Extended) uses a variant of Normal Form D in which
U+2000 through U+2FFF, U+F900 through U+FAFF, and U+2F800 through
U+2FAFF are not decomposed (this avoids problems with round trip
conversions from old Mac text encodings).
http://developer.apple.com/library/mac/qa/qa1173/_index.html
Therefore fix r42457 to exclude the range.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42498 b2dd03c8-39d4-4d8f-98ff-823fe69b080e