Optionally disable METIS

[rhl-]

Similar to #208 we should consdering having the ability to disable METIS as well. There does not appear to be an existing windows build of METIS.

[poulson]

METIS currently does not have a replacement in Elemental and it would be problematic to remove it. The current METIS build issues have to do with symbol exporting and I have a 90% finished port that needs to be finished.