* lib/racc/parser.rb: reverted r65505.  require_relative does
  not work for racc/cparse.so, as extension libraries are placed
  in other directories than Ruby libraries.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@65514 b2dd03c8-39d4-4d8f-98ff-823fe69b080e