- `spack graph --static` (and `spack.graph.dot_graph`) now do the "right
thing" and print the possible dependency graph of provided packages.
- `spack graph --static` no longer concretizes specs, as it only relies
on class level metadata
- Previously the behavior was not consistent -- `spack graph --static`
would graph possible dependencies of concrete specs, but would only
include some of them. The new code properly pursues all possible
dependencies, and allows traversing by different dependency types.
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