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.
I think it's better to be transparent about it than to worry *too* much about the context of the information. I've seen more than a few issues filed over not noticing this behavior – heck, in the last one I saw, the OP said it should be noted in the graphics options. (I had already implemented this before that, but hey.)