Move some code from Branches/OpenCL to trunk, related to threading and OpenCL:

Added Demos/ThreadingDemo showing how to use the cross-platform btThreadSupportInterface under Windows.
Added Demos/ParticlesOpenCL showing how to run the NVidia particle demo under OpenCL implementations by AMD, NVidia and MiniCL (CPU)

Demos/ParticlesOpenCL/shaders.cpp

@@ -0,0 +1,53 @@
+#define STRINGIFY(A) #A
+
+// vertex shader
+const char *vertexShader = STRINGIFY(
+uniform float pointRadius;  // point size in world space
+uniform float pointScale;   // scale to calculate size in pixels
+uniform float densityScale;
+uniform float densityOffset;
+varying vec3 posEye;
+void main()
+{
+    // calculate window-space point size
+    posEye = vec3(gl_ModelViewMatrix * vec4(gl_Vertex.xyz, 1.0));
+    float dist = length(posEye);
+    gl_PointSize = pointRadius * (pointScale / dist);
+//    gl_PointSize = 4.0;
+
+    gl_TexCoord[0] = gl_MultiTexCoord0;
+    gl_Position = gl_ModelViewProjectionMatrix * vec4(gl_Vertex.xyz, 1.0);
+
+    gl_FrontColor = gl_Color;
+}
+);
+
+// pixel shader for rendering points as shaded spheres
+const char *spherePixelShader = STRINGIFY(
+uniform float pointRadius;  // point size in world space
+varying vec3 posEye;        // position of center in eye space
+void main()
+{
+    const vec3 lightDir = vec3(0.577, 0.577, 0.577);
+    const float shininess = 40.0;
+
+    // calculate normal from texture coordinates
+    vec3 N;
+    N.xy = gl_TexCoord[0].xy*vec2(2.0, -2.0) + vec2(-1.0, 1.0);
+    float mag = dot(N.xy, N.xy);
+    if (mag > 1.0) discard;   // kill pixels outside circle
+    N.z = sqrt(1.0-mag);
+
+    // point on surface of sphere in eye space
+    vec3 spherePosEye = posEye + N*pointRadius;
+
+    // calculate lighting
+    float diffuse = max(0.0, dot(lightDir, N));
+//    gl_FragColor = gl_Color * diffuse;
+
+	vec3 v = normalize(-spherePosEye);
+    vec3 h = normalize(lightDir + v);
+    float specular = pow(max(0.0, dot(N, h)), shininess);
+    gl_FragColor = gl_Color * diffuse + specular;
+}
+);