RenderSystemCapabilities extension

[bishopnator]

Hi, I need to test if GPU supports border texture address mode, but in RenderSystemCapabilities there are missing caps for that. I think it will be very useful to add all caps to this class (for "every" method in render system).

For example it is not possible to determine following caps:
* [main caps] max. texture size (it is determined somewhere inside ogre during texture loading)
* dynamic texture support
* [primitive misc caps] hw culling mode support
* [ZCmdCaps] z-buffer comp. caps
* etc. ...

I get some rendering errors on GPU which doesn't support border texture address mode (ATI X600) and it is not possible to fix it without checknig support for that in render system. But now it is not possible to check it. So in general I think that it will be very good to have support for checking every particular capability. I am working only with DX and DX Caps contains a looooot of caps.