Cycles: Add some utility functions and structures

Most of them are not currently used but are essential for the further work.

- CPU kernels with SSE2 support will now have sse3b, sse3f and sse3i

- Added templatedversions of min4, max4 which are handy to use with register
  variables.

- Added util_swap function which gets arguments by pointers.
  So hopefully it'll be a portable version of std::swap.

intern/cycles/kernel/kernel_compat_cpu.h

@@ -344,6 +344,12 @@ typedef texture_image<uchar4> texture_image_uchar4;
 
 #define kernel_data (kg->__data)
 
+#ifdef __KERNEL_SSE2__
+typedef vector3<sseb> sse3b;
+typedef vector3<ssef> sse3f;
+typedef vector3<ssei> sse3i;
+#endif
+
 CCL_NAMESPACE_END
 
 #endif /* __KERNEL_COMPAT_CPU_H__ */