Add floor32, ceil32, round32 compatibility functions for burnings renderer.

To avoid changing burnings now those functions have no IRRLICHT_FAST_MATH anymore, 
there's a new header irrMathFastCompat.h which has ..._fast functions doing the old behavior.
With the troubles they have documented.
I changed burnings to use those functions throughout.
Or as much as possible... Burnings probably also uses classes like SColor which also have functions 
using those, but I don't plan  to adapt them.
Maybe IRRLICHT_FAST_MATH should be a flag exlusive to burnings in the future, I don't think it makes 
much sense otherwise anymore (it often expects 32-bit asm).

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6012 dfc29bdd-3216-0410-991c-e03cc46cb475

source/Irrlicht/SoftwareDriver2_helper.h

@@ -12,6 +12,7 @@
 
 #include "SoftwareDriver2_compile_config.h"
 #include "irrMath.h"
+#include "irrMathFastCompat.h"
 #include "CSoftwareTexture2.h"
 #include "SMaterial.h"