Also fixed texture names, which could have spaces and thus fail immediately upon loading. Now the path is given relative to the .mtl file, which often works, and in case of spaces in the path no path at all is used.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4467 dfc29bdd-3216-0410-991c-e03cc46cb475