testing gravity in tests/bowling.lua, updated ag.setGravity() documentation

git-svn-id: svn://anubis/anaglym/trunk@201 99a6e188-d820-4881-8870-2d33a10e2619

doc/index.html

@@ -398,6 +398,7 @@ The default up vector is (0, 0, 1).
 <p><tt>ag.setGravity(gx, gy, gz)</tt></p>
 <p>
 This function sets the gravity vector to (gx, gy, gz).
+The default gravity vector is (0, 0, -9.81).
 </p>
 
 <a name="ag_startFrame" />