- Improved mipmaps handling (this modification was required for better support of cube maps and texture arrays in near future).
- Set IImage::lock and IImage::unlock methods as deprecated (those method names was wrong, IImage::unlock did nothing...). Please use IImage::getData method instead of older alternatives.

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@5168 dfc29bdd-3216-0410-991c-e03cc46cb475