fix some warnings, disable gimpact by default in world importer,

use DIRECTLY_UPDATE_VELOCITY_DURING_SOLVER_ITERATIONS by default for now,
until we find the issue with some failing test cases in btMultiBody
fix a crashing issue in MyMultiBodyCreator.cpp (uninitialized variable)
disable excessive debug printf in URDF2Bullet

examples/BasicDemo/main.cpp

@@ -24,7 +24,6 @@ subject to the following restrictions:
 
 int main(int argc, char* argv[])
 {
-	struct PhysicsInterface* pint = 0;
 	
 	DummyGUIHelper noGfx;