only rerun when at least one test failed

.travis.yml

@@ -19,7 +19,7 @@ script:
   - # get a list of all of the failed tests into this stupid ctest format
   - python -c 'fn = "Testing/Temporary/LastTestsFailed.log"; import os; os.path.exists(fn) or exit(0); l = [line.split(":")[0] for line in open(fn)]; triplets = zip(l, l, [","]*len(l)); print "".join(",".join(t) for t in triplets)' > FailedTests.log
   - # rerun all of the failed tests
-  - ctest -I FailedTests.log
+  - [[ -s FailedTests.log ]] && ctest -I FailedTests.log
   - # run the python tests too
   - cd python/tests
   - nosetests -vv