Use a more reliable method to get x,width for visual block selection

This works well with the default font on my system, but for some
reason with Inconsolata 17pt, what I normally use in my editor,
the x position gets more and more "behind" the further from
column 0 the cursor gets. This makes no sense because I'm
explicitly asking for the row bounds from the STYLED text
widget. But, at least it's more accurate than the previous
implementation which would could get *way* off....
Merge branch 'master' of github.com:vrapper/vrapper