[CMake] FindFLTK behavior changes between Ubuntu 14.04 and 15.10

[Rob McDonald]

On Ubuntu 14.04 (CMake 2.8.12.2), FindFLTK.cmake sets
FLTK_FLUID_EXECUTABLE to '/usr/bin/fluid'.  This is good.

On 15.10 (CMake 3.2.2), FLTK_FLUID_EXECUTABLE gets set to 'fluid'.  This is bad.

An eyeball comparison of the FindFLTK.cmake scripts included with each
doesn't reveal anything suspicious.  On another mailing list, someone
suggested that the root cause of the change could be a change in bash
behavior.

Does anyone know what caused this?  Does anyone have a workaround?

Is there a way to set the CMake variable to the result of a 'which' command?

Thanks for any help,

Rob