Update geo_homogeneous test, add eval() to PermutationMatrix.

It's the test that's broken, not the functionality. The problem is returning an expression involving Random(). Every time the original expression was evaluated, it generated a new random vector, triggering different results in the comparison. Explicitly valuating the random vector first before calling .homogenous() fixes this.

Also added an eval() method to PermutationMatrix for consistency with DenseBase. Otherwise, you would need to call different functions on different expressions to express the same thing.