Update some setting descriptions in the graphics options. Hide "Disable Destination Alpha" from wx UI.

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.
Everyone says XFB, on the forums, IRC, and even <i>in the code right there</i>. I definitely think mentioning it in the emulator UI helps here.