Blender Git Loki

* Change to the working of the left mouse select preference

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.