[vtkusers] vtkCarbonRenderWindow and existing PowerPlant windows

[James Dessart]

I've gotten a little clearer on this... the CarbonRenderWindow sets the
refcon on the mac window to itself, which, in the future, is retrieved by
the CarbonRenderWindowInteractor.  However, PowerPlant ALSO uses the
window's refcon to store its object associated with the window.  So it
doesn't make any sense for both to use it, since it's only a single
variable.

Here's my proposed change, which I will use in my own copy of the code,
and which may be useful for anyone trying to use VTK in conjunction with
PowerPlant and CodeWarrior.  I have added a define of VTK_USE_PP, which
should only be defined if VTK_USE_CARBON is valid.  It also means the
CarbonRenderWindowInteractor would be useless, but I'll come up with a
PowerPlant interactor, if I can get the rendering working properly.

Anyways, if VTK_USE_PP is defined, the refcon will not be set by the
RenderWindow.

Not sure if this works fully yet, but I'll keep you guys posted.  If
anyone has feedback on this, or is interested in knowing what it takes to
get VTK compiling in CodeWarrior for Mac OS X, just ask.

Oh, and here's an interesting factoid, with precompiled headers in
CodeWarrior, a semi-complete VTK build (png and freetype parts removed)
takes at most a half hour on my dual 400mhz G4 (with 768 MB RAM)

James