Muelu

This pull request adds MueLu as a preconditioner. The pull request is not ready to be merged, I'm waiting for upstream to fix a bug. For now the code works exactly in the same way as ML, except for the parameter high_order_function which does not exist anymore. There is also a lot of code which is commented that can be used when we want to break compatibility with ML.
Wolfgang, this refers to the index type of the Epetra matrix so it should be correct. And if I remember the MueLu status correctly, it only works with the 32-bit interfaces of Epetra.