[ODE] constructor problem in collision_trimesh.cpp

[steve1011]

I think the problem is that dUASSERT is usually used inside processing 
functions where the variable 'g' is defined as an object. It's not 
defined in the constructor and causes a compile error. I think the 
intent was to use dUASSERT to report at run time if the dxTriMeshData 
class is instantiated when the libraries were compiled with trimesh 
disabled. I didn't find the definition for dUASSERT so I don't know if 
my 'fix' of removing the variable g and replacing it with the value 0 is 
proper. I looked for an example of an ASSERT that took only a string 
argument but didn't find it.