[Cmake] Hiding Includes

[Brad King]

> . Including an installed VTK (in /usr/local/include/vtk)  generates
>   a correct  -I /usr/local/include/vtk
>   a correct  -I /usr/local/gnu/include     (for OpenGL)
>   a spurious -I /usr/local/include

How did you install VTK?  When VTK builds, it keeps track of all the
include directories on the system that it needed for headers included by
its headers.  Something VTK needed must have been found in
/usr/local/include.  Look in VTK's CMakeCache.txt file to see what
requires it.

-Brad