add the BT_ prefix for all #ifdef guards, to avoid conflicts with developers own header defines.

Fixes Issue 497

//license header
#ifndef BT_RIGIDBODY_H
#define BT_RIGIDBODY_H
class btRigidBody
{
};
#endif //BT_RIGIDBODY_H

src/LinearMath/btList.h

@@ -14,8 +14,8 @@ subject to the following restrictions:
 
 
 
-#ifndef GEN_LIST_H
-#define GEN_LIST_H
+#ifndef BT_GEN_LIST_H
+#define BT_GEN_LIST_H
 
 class btGEN_Link {
 public:
@@ -67,7 +67,7 @@ private:
     btGEN_Link m_tail;
 };
 
-#endif
+#endif //BT_GEN_LIST_H