Merged new versions of libpng and jpeglib from vendor branch. Had to fix some minor things in JPG reader and the jconfig.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4823 dfc29bdd-3216-0410-991c-e03cc46cb475
Make the output-listbox for filesnames a little bit larger as otherwise only short paths did get displayed.
Also add output for selecting a directory (was mainly needed for bug-hunting, but I guess won't hurt having that always).

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4824 dfc29bdd-3216-0410-991c-e03cc46cb475