In Ruby 1.9.3 `#b` is not defined. The change I made to Rack (see
rack/rack@b62cd8a) and Rails (see rails/rails#29062) won't work for Ruby
1.9.3 because of this.

For less than Ruby 2.0 we should skip the
`test_normalize_path_maintains_string_encoding` test because it won't
pass. `#b` will always be undefined for the Rack dependent change, and
since the Rack change isn't present then Rails will see a bad request
instead of a not found for the routing test.

For the routing test we should handle it differently if it's Ruby 1.9.3
(because then the behavior is clear). Ruby 1.9.3 will always return a
bad request because we can't fix the problem in Rack. The routing test
asserts the requests return a bad request in Ruby 1.9.3 or return the
appropriate response in Ruby 2.0.0 and above.