Improve assertion for access to nonlocal elements

Improve assertion in Trilinos vectors: Previously, we used 'local_range()' from within the assertion message, which creates an assertion in itself and giving the user no clue where the error actually happened. I also included the number of local elements in the error message to be more specific on what goes wrong.
This is preexisting, so not your fault, but if we are sure that we want to return zero instead of throwing the exception, then the commented out exception should just be deleted.