EMT_TRANSPARENT_ALPHA_CHANNEL_REF working again like in older Irrlicht versions (1.4 or so):
It uses again SMaterial::MaterialTypeParam instead of a hardcoded values and makes an exception when MaterialTypeParam is 0 (using it like 0.5 instead) to ensure it works by default. See http://irrlicht.sourceforge.net/forum/viewtopic.php?f=7&t=48940 for new discussion.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4569 dfc29bdd-3216-0410-991c-e03cc46cb475