a character is not found properly.
* string.c (rb_enc_strlen): round up string length with fixed
multibyte encoding such as UTF-32.
(rb_enc_strlen_cr): ditto.
(rb_str_substr): fix substring with fixed multibyte encoding.
(rb_str_justify): check number of characters.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@15573 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
