Trackbar size fixes

[BiGgUn]

> winuser.h:#define SM_CYCAPTION         4

Sorry, I was wrong. 
In the standard Windows Metrics, GetSystemMetrics( SM_CYCAPTION) returns 19.
The thumb length equals this value + 2. 

infoPtr->uThumblen = GetSystemMetrics( SM_CYCAPTION) + 2;

On a native platform, if you modify this value, thumb length will follow this formula.

But it is not so simple, there are other conditions for computing the initial thumb length.

Stephan