Added getbyte as a core_ext to Ruby < 1.9

Signed-off-by: José Valim <jose.valim@gmail.com>

activesupport/lib/active_support/core_ext/string/conversions.rb

@@ -28,6 +28,10 @@ def ord
     self[0]
   end unless method_defined?(:ord)
 
+  def getbyte(index)
+    self[index]
+  end if RUBY_VERSION < '1.9'
+
   # Form can be either :utc (default) or :local.
   def to_time(form = :utc)
     return nil if self.blank?

activesupport/test/core_ext/string_ext_test.rb

@@ -110,6 +110,14 @@ def test_ord
     assert_equal 97, 'abc'.ord
   end
 
+  if RUBY_VERSION < '1.9'
+    def test_getbyte
+      assert_equal 97, 'a'.getbyte(0)
+      assert_equal 99, 'abc'.getbyte(2)
+      assert_nil   'abc'.getbyte(3)
+    end
+  end
+
   def test_string_to_time
     assert_equal Time.utc(2005, 2, 27, 23, 50), "2005-02-27 23:50".to_time
     assert_equal Time.local(2005, 2, 27, 23, 50), "2005-02-27 23:50".to_time(:local)