Slow perfomance on linux (Ubuntu Dapper)

[eranif]

I am currently updating wxFlatNotebook to work with renderers, so it is a a good opertunity for some maintenance, the OnPaint function is getting too big to handle (not to mention that it is a correct design to work with abstaract renderer, this way adding new styles is *much* easier)

I will try to remove redundant text calculations where I can.
Eran