Add option to testharness to read list of tests from file
Add option to testharness to read list of tests from file

When working on a new feature, we may introduce a small set of failing
tests.  Since running the entire test suite may take a long time, we'd
like (when debugging the failures) to only run a subset of tests.  A
new option --from-file in testharness allows us to specify a list of
tests to run in a file (one per line).

rjferrier/fluidity,jrper/fluidity,jjo31/ATHAM-Fluidity,jjo31/ATHAM-Fluidity,jrper/fluidity,rjferrier/fluidity,rjferrier/fluidity,jrper/fluidity,iakovos-panourgias/fluidity,jrper/fluidity,iakovos-panourgias/fluidity,iakovos-panourgias/fluidity,rjferrier/fluidity,jrper/fluidity,rjferrier/fluidity,jjo31/ATHAM-Fluidity,iakovos-panourgias/fluidity,iakovos-panourgias/fluidity,jjo31/ATHAM-Fluidity,jjo31/ATHAM-Fluidity