Merge Onigmo 27278c12e6674043cc8affca6507e20e119a86ee.

* regparse.c (is_onechar_cclass): [bug] unexpected match occurs when a
  char class contains no char

* enc/unicode.c (init_case_fold_table): define the sizes of case
  folding tables in casefold.h

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@34860 b2dd03c8-39d4-4d8f-98ff-823fe69b080e