added Steven Baker's GPU physics code (work in progress)

Extras/GPUphysics/DEBUGGING_README

@@ -0,0 +1,67 @@
+
+I have added some command line options to hopefully
+help with our debugging problems.
+
+1) Run without any shaders at all:
+
+    GPU_physics_demo -s
+
+   This should produce a grey screen with a neat grid of randomly
+   coloured cubes that are sitting completely motionless.  If this
+   doesn't work then render-to-texture and shaders are not the
+   problem and we have some very basic OpenGL problem to worry
+   about.
+
+2) Run with just one shader - but no render-to-texture:
+
+    GPU_physics_demo -p
+
+   Just like '-s', this should produce a grey screen with a neat
+   grid of randomly coloured cubes that are sitting completely
+   motionless.  This time, the vertex shader is reading the
+   positioning information from a texturemap.  If this
+   doesn't work then render-to-texture isn't the problem but
+   something is amiss in shader-land.
+
+   There are several possibilities - the nastiest of which might
+   be that either:
+
+   a) Your graphics card/driver doesn't support floating point
+      textures.  (This is pretty much 'Game Over' for you because
+      without that, doing physics in the GPU is going to be
+      virtually impossible).
+
+   b) Your graphics card/driver doesn't support vertex shader
+      textures (or it supports them but sets the maximum number
+      to zero - which is the same thing).  This means that we
+      can't move things around using GPU textures - but we can
+      still use the GPU to accellerate physics calculations.
+      In practical game scenarios, I think the CPU needs to know
+      where all the objects are - so this may not be the serious
+      issue it sounds like.  What it mostly does is to clobber
+      the idea of running physics on particle system types of
+      effect where a vast number of objects are involved but
+      where individual objects have zero effect on game play.
+
+3) Run without forces being applied:
+
+     GPU_physics -f
+
+   This sets the cubes off moving at constant speed (each cube
+   going at a different speed and spinning).
+
+   Run without collision against the ground:
+
+     GPU_physics -c
+
+   The cubes move under gravity - but don't interact with the
+   notional ground plane so the eventually fall off the bottom
+   of the screen..
+
+   If either (3) or (4) fails but (1) and (2) worked then the
+   problem is probably something to do with render-to-texture.
+
+   This is the most likely scenario.
+
+
+