Modify Exercise_1.5.

A little adjustment.

Thank you!
							Lawrence R. Amlord
							   Mar. 30, 2013
							   Xi'an, China
Add Exercise_1.6.

Exercise_1.6 is both tough and interesting. It explains the reason why primitive conditional 'if'
can not be replaced by a compound procedure indirectly. Again, it took me half a day to hack it.

Included are the following 3 files:

	Exercise_1.6.pdf
	Exercise_1.6.scm
	Exercise_1.6.tm

Thank you!
								Lawrence R. Amlord
								   Mar. 30, 2013
								   Xi'an, China