[vtkusers] VTK Builds on Cygwin

[Bill Hoffman]

Hi all,

I have just checked in changes to configure and the makefiles of 
VTK to allow the cygwin compiler to be used to build VTK. 
Thanks to Mumit Khan for doing most of the work.

To build with cygwin, just follow the unix build instructions for 
VTK. Both shared and static work. VTK uses the native windows 
OpenGL libraries so acceleration is possible.
You will want the most recent version of cygwin.

-Bill