test_string.rb: yet another test

* test/ruby/test_string.rb (TestString#test_frozen_string_adjacent):
  option is allowed after the last string.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42780 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
Enhance Numeric#step.

* numeric.c (num_step): Default the limit argument to infinity and
  allow it to be omitted.  Keyword arguments (by: and to:) are
  introduced for ease of use. [Feature #8838] [ruby-dev:47662]
  [ruby-dev:42194]

* numeric.c (num_step): Optimize for infinite loop.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42781 b2dd03c8-39d4-4d8f-98ff-823fe69b080e