* string.c: use long allocator names instead of numbered
  allocator names.
  * rb_str_new2 -> rb_str_new_cstr
  * rb_str_new4 -> rb_str_new_frozen
  * rb_str_new5 -> rb_str_new_with_class
  * str_new3 -> str_new_shared
  * str_new4 -> str_new_frozen_with_klass



git-svn-id: svn+ssh://svn.ruby-lang.org/ruby/trunk@44808 b2dd03c8-39d4-4d8f-98ff-823fe69b080e