Use size_t for file size instead of unsigned int

This is one step to help us open files with more then 4 GB size.

code/AssetLib/STL/STLLoader.h

@@ -109,7 +109,7 @@ protected:
     const char* mBuffer;
 
     /** Size of the file, in bytes */
-    unsigned int mFileSize;
+    size_t mFileSize;
 
     /** Output scene */
     aiScene* mScene;