Take the Windows taskbar into account when deciding on the maximum

Take the Windows taskbar into account when deciding on the maximum
size of the puzzle window. This has involved some _completely
stupid_ window manipulation: in order to figure out in advance how
big I want my main window to be, I first have to _create_ the status
bar so I know how tall it is; but since I can't reparent it into my
main window after I've created it, I then have to throw that status
bar away and create a new one. *sigh*

[originally from svn r6276]