Makes more sense to ask about method_defined?

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

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

@@ -30,7 +30,7 @@ def ord
 
   def getbyte(index)
     self[index]
-  end if RUBY_VERSION < '1.9'
+  end unless method_defined?(:getbyte)
 
   # Form can be either :utc (default) or :local.
   def to_time(form = :utc)