[CMake] Graphviz support in CMake

[Andy Cedilnik]

Hello,

I got tired of tracing dependencies between libraries by hand, so I 
added support in CMake to dump out a graphviz file of all dependencies 
between libraries. Example can be seen here:

http://www.cmake.org/Wiki/CMake:For_CMake_Hackers

To use it, run cmake in the build tree:

cmake --graphviz=test.dot .

Ok, current issues:
1. If you have too many targets (like VTK, ITK, and pretty much anything 
else) you will not see anything
2. All things are same color, so no way to differentiate
3. No differentiation between full path to the library and library itself
4. Layout could be improved

Look at it and give me suggestions.

-- 
Andy Cedilnik
Kitware Inc.