* ruby.c (load_file_internal, ruby_process_options): share
  ruby_engine instead of literal strings.

* version.c (Init_version): remove internal `ruby_engine_name`,
  but set the VM program name in addition to the global constant.

* vm_backtrace.c (location_to_str, oldbt_init): use th eVM program
  name always.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@52782 b2dd03c8-39d4-4d8f-98ff-823fe69b080e