Change from dimension2d<s32> to dimension2d<u32> where practical. IImage and ITexture now have unsigned dimensions, as does screen size. This has had a significant knock-on through the code base, but it is more technically correct - the BEST KIND of correct.
GUI elements and draw2DImage methods still have and take signed dimensions, but we can look into this in future. Regression tested with the test suite and the example apps. Note that createDevice() now takes dimension2d<u32>!
git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@2092 dfc29bdd-3216-0410-991c-e03cc46cb475
