The symptom was exceptions while creating physical terrain.
Reduce default terrain mesh magnification to 2 from 3 because the
higher resolution uses a lot of memory and doesn't solve the terrain
smoothness for vehicles.
Added comments here and there and improved some debugging log messages.
for the operation of BulletSim and those defintiions/structures defined
so they can be used in the unmanaged world.
Consolidate setting of collision flags so implementation is not scattered.
While fixing the above, add methods to physical body and shape pointer
wrapper so routines won't have to know that IntPtr.Zero means no
physical instance.
Fix problem with physical linksets failing after a few sits and
unsits by properly restoring child prom positions for compound
linksets after multiple selection and deselections.
static objects by more restrictive selection of objects that collide
with static objects.
Rename collision mask fuctions from 'filter' to 'group' so it is clear
what is being set.
Rename BulletSimAPI.SetCollisionFilterMask() to SetCollisionGroupMask to match above.
Restore passing of time step to linear and angular motion component routines.
Use buffering vehicle physical parameter get/set routines consistantly.
Make range enforcement clearer by using ClampInRange() function for parameter setting.
Remove commented out experimental vehicle calculations.
