cache quoted column names in SQLite3

we do this in other adapters, and it's a nice speed improvement

activerecord/lib/active_record/connection_adapters/sqlite3_adapter.rb

@@ -121,6 +121,7 @@ def initialize(connection, logger, connection_options, config)
         @config = config
 
         @visitor = Arel::Visitors::SQLite.new self
+        @quoted_column_names = {}
 
         if self.class.type_cast_config_to_boolean(config.fetch(:prepared_statements) { true })
           @prepared_statements = true
@@ -240,7 +241,7 @@ def quote_table_name_for_assignment(table, attr)
       end
 
       def quote_column_name(name) #:nodoc:
-        %Q("#{name.to_s.gsub('"', '""')}")
+        @quoted_column_names[name] ||= %Q("#{name.to_s.gsub('"', '""')}")
       end
 
       #--