Detector for unused variables

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I wrote a short programm which detect and list unused variables.
I'm sure it isn't perfect but it passed most of my test cases, 
but I think at the moment it isn't good enough to present it in 
announce. Maybe some of you have interest to help me. IMO 
something like this should be integrated into the D compiler.

Comments, suggestions and critism are desirable.

Code: http://dpaste.dzfl.pl/c5f1d2ba
Some of my testcases: http://dpaste.dzfl.pl/f74da85e