Issue with display of contents in rounded views

[nick87720z]

Includes two issues, which are betst visible with some rounding.

1. When border gets rounding, its orthogonal sides are placed on some distance from contents so, that rounding arc goes through unrounded contents angle.
2. Even if 1st is fixed, it will not look good if contents is above border.

Oxygen is one good example, how to do it. No idea how, may be ony contents background is expanded, but foreground is not. But i don't see problem if foreground will be covered with such small rounding, as now.

Affects both qt4 and gtk2 (twf behind designer)