Irrlicht generally avoided user pointers in the past, but after trying all kind of ugly workarounds - this is just easier and
not that much downsides really. Tiny speed costs due to additional SMaterial memory size and new comparison tests.
But allows to keep SMaterial alive and useful for a while longer without needing a complete rewrite and it can now be used for stuff like writing PBR shaders.
Using a new interface io::IUserData for this which also allows serialization the user data (that part is untested so far, sorry)
git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6567 dfc29bdd-3216-0410-991c-e03cc46cb475
Usually something like __IRR_SOME_GUARD_INCLUDED__ replaced by IRR_SOME_GUARD_INCLUDED.
Removing underscores at the end wasn't necessary, but more symmetric (probably the reason they got added there as well).
While this touches every header it shouldn't affect users (I hope).
Also a few whitespace changes to unify whitespace usage a bit.
And a bunch of spelling fixes in comments.
git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@6252 dfc29bdd-3216-0410-991c-e03cc46cb475
