fix some issues with Linux compatibility,

see Issue 409

Demos/ParticlesOpenCL/MiniCL/CMakeLists.txt

@@ -8,6 +8,10 @@ ${BULLET_PHYSICS_SOURCE_DIR}/Demos/OpenGL
 
 ADD_DEFINITIONS(-DUSE_MINICL)
 
+#to get this to compile under linux, you could try setting CMAK_GLEW_LIBRARY
+#to  /usr/lib/libGLEW.so
+
+
 IF(WIN32)
 IF (CMAKE_CL_64)
 	SET(CMAK_GLEW_LIBRARY	${BULLET_PHYSICS_SOURCE_DIR}/Glut/glew64.lib	)

Demos/Raytracer/Raytracer.cpp

@@ -491,7 +491,7 @@ extern unsigned char sFontData[];
 	if (0)
 	{
 
-		char* text="ABC abc 123 !@#";
+		const char* text="ABC abc 123 !@#";
 			int x=0;
 		for (int cc = 0;cc<strlen(text);cc++)
 		{

Demos/ThreadingDemo/main.cpp

@@ -24,9 +24,10 @@ void	SampleThreadFunc(void* userPtr,void* lsMemory);
 void*	SamplelsMemoryFunc();
 
 #include <stdio.h>
+#include "BulletMultiThreaded/PlatformDefinitions.h"
 
-
-#ifdef __APPLE__
+#ifdef USE_PTHREADS
+//#ifdef __APPLE__
 #include "BulletMultiThreaded/PosixThreadSupport.h"
 
 btThreadSupportInterface* createThreadSupport(int numThreads)