graphviz:
* Download from Fedora projet, as main graphviz site not working.
* Disable java because Spack does not yet support Java, and the system might not have it installed.
* Added all language binding variants; disabled enough in the default configuration to avoid dependencies.
* Removed alternate download location (turned into comments).
* Turn off all language bindings by default.
* Raise an exception on bindings that have not been verified to work.
* Added text indicating what works and doesn't work when user runs `spack info`.
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