Patch to make vertical BSliders work

[Pete]

I guess I'm the first person to have actually needed vertical sliders, but found that they worked very badly in my ported BeOS app. (I see Stippi noted this three years ago, but apparently got sidetracked...)

The attached patch fixes the observed problems:

Height of sliders was never more than 100 pixels

Slider bar fill colouring didn't work

The triangle thumb (in ControlLook) wasn't rotated

(I notice that Haiku triangle thumbs are on the right, while BeOS had them on the left. I vaguely find the Haiku convention more natural, so I didn't mess with that.)

[Pete]

Patch for Slider.cpp and ControlLook.cpp

[stippi]

Patch looks fine, thank you!

[stippi]

Applied with coding style corrections in hrev41881 (you probably get merge conflicts when you update, please have a look at what I changed). Thanks for your work, greatly appreciated!