#303 irrlicht deffered texture loader for asynchronous scene loading

[ovan spaki]

loading scene asynchronously already work, but texture upload fail,
because @genTexture is generated on ITexture constructor on the second thread
that result of the texture can be displayed/updated

this patch cache all query @createDeviceDependentTexture by creating a FakeTexture on the memory, this one as the same size of COpenglTexture to allow to reuse the texture adress when the cache is cleared.

so all adresse related to the new object doesn't change, and all just work fine
thank you

ps: this patch provide an implementation for and only for COpenglDriver (at this time)
original source: http://irrlicht-fr.org/viewtopic.php?pid=11697#p11697 and http://irrlicht.sourceforge.net/forum/viewtopic.php?f=2&t=50900#p296073

ps2: just use setDeferredTextureLoader(true) before the loading thread and setDeferredTextureLoader(false) after to clean up the cache and upload all texture