* app/appenv.h: Define ROUND(), RINT(), SQR(), G_PI and
	G_PI_4. The latter two will presumably eventually be in
	GLib. RINT() calls rint() if we have it, otherwise adds 0.5 and
	calls floor().

	* app/*.c: Remove the multiple identical definitions of M_PI. Use
	G_PI instead of M_PI. Remove ROUND() and rint() definitions. Use
	RINT() instead of rint().