Added a check method to query the device reset event for D3D drivers. Since in the case of a reset the content of all RTTs are lost, it's required to become aware of this fact.
The current solution is just a simply check which works with lots about the drivers. A cleaner solution would return all structures which have to be regenerated. A new enum is already created for this reason, but not yet implemented. However, the interface of the new checkDriverReset method might change in the near future...

git-svn-id: svn://svn.code.sf.net/p/irrlicht/code/trunk@1630 dfc29bdd-3216-0410-991c-e03cc46cb475