Merge branch releases/1.8 revisions 4828:4923 into trunk:
- Fix bug with multiple SetPixelFormat calls.
- Fixed bug related to memory release in PNG image loader. Thanks elephoenix for it.
- Fix crash in CGUIListBox when users pressed end key folled by any other key in an empty, focused list box (thanks at porcus for report and patch).
- Fix use of enabling defines for wal2 (halflife) image loader. Thanks to hendu for noticing.
- Fix proper screenshot creation in test by inserting the stabilizeScreenBackground call.


git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@4925 dfc29bdd-3216-0410-991c-e03cc46cb475