Estimated hours taken: 0.25
tests/invalid/Mmakefile:
Allow tests to pass if the output matches either the .err_exp
file or the .err_exp2 file (if any).
tests/invalid/missing_interface_import.err_exp2:
Add an alternative expected output for this test case,
since the output is different depending on whether
or not it gets compiled with --use-subdirs.
