Fixed Deled texture search. The scene parameter DMF_USE_MATERIALS_DIR was renamed to DMF_IGNORE_MATERIALS_DIR with opposite meaning, because the default should be to use the directory defined in the file.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@2487 dfc29bdd-3216-0410-991c-e03cc46cb475