add test for pipes with external commands.
add test for pipes with external commands.

Ignore-this: 664e45bd53b8587f4a0624a263eed9dd
The only external command I use is shsh itself, since it's the only
program we are certain is present...

darcs-hash:20081121171559-72aca-4f088d0126991da6d490cfd85397af3f754f25ae

shicks/shsh,shicks/shsh