Add required argument dataset to sql_literal. Add alias sql_literal f…

…or to_s.

lib/sequel/dataset/sql.rb

@@ -810,12 +810,15 @@ def literal_integer(v)
       v.to_s
     end
 
-    # SQL fragmento for a type of object not handled by Dataset#literal.
+    # SQL fragment for a type of object not handled by Dataset#literal.
     # Calls sql_literal if object responds to it, otherwise raises an error.
+    # Classes implementing sql_literal should call a class-specific method on the dataset
+    # provided and should add that method to Sequel::Dataset, allowing for adapters
+    # to provide customized literalizations.
     # If a database specific type is allowed, this should be overriden in a subclass.
     def literal_other(v)
       if v.respond_to?(:sql_literal)
-        v.sql_literal
+        v.sql_literal(self)
       else
         raise Error, "can't express #{v.inspect} as a SQL literal"
       end

lib/sequel/sql.rb

@@ -49,6 +49,11 @@ def self.to_s_method(meth, args=:self) # :nodoc:
       def lit
         self
       end
+
+      # Alias for to_s
+      def sql_literal(ds)
+        to_s(ds)
+      end
     end
 
     # Represents a complex SQL expression, with a given operator and one