Missing math.h in testsprite.c

Hello !

I get a warning compiling testsprite.c in the test dir. because it has
no math.h included, so the sin function is unknown :

http://www.libsdl.org/cgi/cvsweb.cgi/SDL12/test/testsprite.c?rev=1.5&content-type=text/x-cvsweb-markup

CU