Start on llvm test script...
Add -llvm flag and llvm support to nightly script.
Run hellos and extern/ferguson for llvm testing.
Use comm=none instead of gasnet.
word smithing
Merge pull request #395 from thomasvandoren/llvm-test-script

Add support for running automated tests with llvm.

Update nightly to support new -llvm flag, which adds --llvm to start_test compopts. Also add new
testing script that runs the hellos and extern/ferguson tests (these were requested by @mppf).

reviewed by @ronawho