[CMake] Suggesting to FindQT4.cmake where to find QT4

[Alexander Neundorf]

On Friday 29 May 2009, Clinton Stimpson wrote:
...
> Yes, that's doable right now.
> But, I was actually hoping for something that worked automatic like
> CMAKE_PREFIX_PATH.
> Not something extra people have to code into their Find*.cmake files or
> extra things they have to do with their find_* calls.
> Also, I was thinking of a cmake variable, not an environment variable.

That sounds like a reasonable idea.
I would suggest to use this when find_package(Foo) is used, i.e. that 
find_package(Foo) would check if there is a Foo_ROOT_DIR cmake variable is 
set (which could be initialized from an eventually set env. var. 
Foo_ROOT_DIR) and use this as the first dir to check.

Alex