pack.c: refine warning
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65748 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
pack.c: refine warning
directive in unpack too, and quote unprintable characters.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65748 b2dd03c8-39d4-4d8f-98ff-823fe69b080e