* range.c (range_step, range_each): String#upto should never
  modifies the receiver, use frozen strings to enumerate symbols.

* re.c (reg_operand): matching target is not modified.

* ext/socket/constants.c (constant_arg): str_to_int never modifies
  argument strings.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50306 b2dd03c8-39d4-4d8f-98ff-823fe69b080e