Ruby

extconf.rb: git rid of post-1.8 feature

• ext/digest/*/extconf.rb, ext/openssl/extconf.rb: get git rid of
  post-1.8 feature require_relative for cross compilation.
  [ruby-core:50160] [Bug #7439]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@37878 b2dd03c8-39d4-4d8f-98ff-823fe69b080e