Add code in section 2.5.2.

Included are the following file:

	Combining_Data_of_Different_Types.scm

Thank you!
							Lawrence R. Amlord
							   Jul 29th, 2013
							   Xi'an, China
Update code of section 2.4.3.

Modified is the following file:

	Data-Directed_Programming_and_Additivity.scm

Thank you!
							Lawrence R. Amlord
							   Jul 29th, 2013
							   Xi'an, China