In 4774 we tried fixing zwriting for shader materials as those are ignored in SMaterial::isTransparent.
This affected too many existing projects and made it hard to still write to zbuffer in some situations where it was necessary. So trying now another approach which brings back old functionality mostly, but allows users to have more fine-control with a new flag. Using an enum instead of bool for the new flag as it's foreseeable that more options might be necessary for this in the future.
Note: Several tests are currently failing, but they did that before, so that has to be debugged on it's own.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@5076 dfc29bdd-3216-0410-991c-e03cc46cb475