[Lazarus] Lazarus: make buttons accessible on Windows

[Lubos Pintes]

Hi,
Currently the buttons in Windows version of Lazarus are not accessible, 
more precisely, they are unnamed. This means that screen reader reads 
all buttons as "button", not "ok button", "cancel button" etc.

This "code contribution" fixes this:

class procedure TWin32WSBitBtn.SetText(const AWinControl: TWinControl; 
const AText: string);
begin
   TWin32WSWinControl.SetText(AWinControl, AText);
   ...
end;

So just inserting one line. I tested it and it works. So if this will be 
accepted, we have buttons accessible on Windows wow. :)