[Cmake] Problems with LatestRelease

[Lorensen, William E (Research)]

I just updated to LatestRelease yesterday. Ineeded to so the the vtk nightly would build. I use the
same cmake for my itk builds. 

itk uses fltk. There is a CMake/Module FindFLTK.cmake. This has not changed recently. The following
problem appeared after the upgrade.

It seems that if a variable, say foo, is not defined, then its substitution is ${foo}. I believe that
in the prior release, no substitution was done and nothing was output.

Here's the example from FindFLTK.cmake...

SET( FLTK_LIBRARY ${FLTK_BASE_LIBRARY} ${FLTK_GL_LIBRARY} ${FLTK_FORMS_LIBRARY} )

There is logic on the cmake file to set FLTK_GL_LIBRARY and FLTK_FORMS_LIBRARY only under certain
conditions. Otherwise they are never set. The CMakeCache.txt file reports ${FLTK_GL_LIBRARY} and
${FLTK_FORMS_LIBRARY} when they are referenced.

Bill