PSD article7:  implementation and tests of Car class in C

New/Changed Files:

car.h:	class definition of Car class in C

car.c:	class implentation of Car class in C

simpletestcar.c:	test program moving a car around and refuelling it

Rest of files unchanged from previous tarball:

vector2.[ch]:	with proper method calls for intra-method calls

simpletestvehicle.c:	test program moving a vehicle around

vehicle.h:	class definition of Vehicle class in C

vehicle.c:	class implentation of Vehicle class in C

vv.[ch]:        "subclass of vector2" that overrides the print method
                to print more info

simpletestvv.c: simple tests for vvs and vector2s, print the answers

testvv.c:	unit tests for vvs and vectors, answers encoded, only
                complains about failures

overrideprint.c: an example which modifies an object's print() method on the fly

testsupport.h:	unit testing support - prototypes and macros

testsupport.c:	unit testing support - functions

simpletestvector2.c: simple tests for vectors, print the answers

testvector2.c:	unit tests for vectors, answers encoded, only complains about failures
