Line tool preview

[LukasT.dev@gmail.com]

Hi,
I noticed little stuff that can be done differently.

Take a look at the method KisToolLine::paintLine(QPainter& gc, const QRect&) 
for painting line-preview when you use line tool:
http://pastebin.com/m2cba0f11

I think that instead of static_cast<int> we could use qRound as it is more 
precise. 0,7 is 0 with static_cast. With qRound 1.

I'm not sure, that's why I'm asking.

If you agree to use qRound, I can commit.
Lukas