Fixed Clang warnings for C++ version.

[ThomasVogelpohl]

Hi Chris,

I got the following warnings from Clang compiler:

b2dJson.cpp: warning: comparison of integers of different signs: 'int' and 'size_type' (aka 'unsigned long') [-Wsign-compare] for (int i = 0; i < m_bodies.size(); i++) { ~ ^ ~~~~~~~~~~~~~~~

b2dJsonImages.h: warning: delete called on 'b2dJsonImage' that has virtual functions but non-virtual destructor [-Wdelete-non-virtual-dtor] delete m_images[i]; ^ I think the reason is that b2dJsonImage_OpenGL is derived type, but destructor of b2dJsonImages.h would be called.

What do you think ? Cheers, Thomas