tests: avoid test-hup hanging on AIX test-hup hangs on AIX. Under ksh89 on AIX (the default shell), echo Hello; while [ ! -s not-there ]; do true; done produces no output while the loop executes. Replacing 'true' with 'sleep 0' fixes, as does using a less broken shell. ksh93 is fine. Update check-code.py to look for this, and make same change in test-serve.t. In fact test-serve works fine, probably because of additional commands between echo and the loop, but that's a subtlety not easy to test for.