Fix warning in is_function_processor_working.
Fix warning in is_function_processor_working.

The path to test_sum.m was wrong. It still works because run_func works
by adding the directory to the path and then calling the function; the
addpath fails with a warning, but test_sum.m is on the path anyway
because it's under matlab/.

arokem/python-matlab-bridge,jjangsangy/python-matlab-bridge,blink1073/python-matlab-bridge,blink1073/python-matlab-bridge,blink1073/python-matlab-bridge,jjangsangy/python-matlab-bridge,arokem/python-matlab-bridge,jjangsangy/python-matlab-bridge,arokem/python-matlab-bridge