Enable the spawn tests to be run from a different directory

[RaymondMichael]

There are a number of spawn tests that assume the program to be spawned is in the current directory. They include function calls like:

MPI_Comm_spawn((char*) "./foo",...);

We run our MPICH tests from a different directory. This causes MPI_Comm_spawn() to fail to find the binaries. We've found that this can be easily fixed if the tests are modified to run argv[0] instead.

[RaymondMichael]

Here's a patch for you.

test_spawn diff.txt