Previously, the implementation of this was quite awkward, with the preference swapping mouse buttons globally, rather than just selection, as is advertised on the pref. This had the effect of changing the painting in sculpt/texture paint/weight paint/etc to the left mouse button. This was totally silly, since when using a tablet, left mouse select is the sane way to go, but it meant that every time you wanted to sculpt or paint, you had to switch the mouse buttons around so you could actually use the tablet as normal. This commit fixes that, and makes the preference do just what it says, use left mouse for selection (i.e. in object/edit mode) and only that.