MPI_ABORT Usage

[JaredCrean2]

The code currently does not use MPI_ABORT when there is an error on one of the processes, and there have been a few instances where MPI jobs have kept running after one process terminates. I think the solution to this is to call MPI_ABORT whenever an assertion/exception is thrown.

[JaredCrean2]

I can see two ways of doing this:

1. create a new @assert macro and new exception types that internally call MPI_ABORT
2. Run the entire solver inside a try catch block that calls MPI_ABORT if an error is thrown

The problem with 1. is that exceptions thrown by code not written by us (for example, the DomainError thrown by the sqrt function in Base) won't call MPI_ABORT.

I don't like 2. because it has the potential to swallow errors that might be recoverable.