Merged r11637 from trunk to 2.3-stable (#13354)

PDF: fix incompatible character encodings: UTF-8 and ASCII-8BIT.

Contributed by Jun NAITOH.

git-svn-id: svn+ssh://rubyforge.org/var/svn/redmine/branches/2.3-stable@11639 e93f8b46-1217-0410-a6f0-8f06a7374b81