Improve some setting descriptions in the graphics options.

More than a few of these have annoyed me for a while, what with their typos and odd wording and occasional lack of important details.

Criticisms welcome. I mean, as long as it doesn't devolve into MORE bikeshedding. Even I don't enjoy that.
Example of why I feel this is necessary: https://code.google.com/p/dolphin-emu/issues/detail?id=7942#c38