merge with stable

alias: fix loss of non-zero return code in command aliases This also includes test for shell aliases. It avoid using "false" command because "man false" does not say "exit with 1" but "exit with a status code indicating failure."

exchange: drop dead code This code have been factorised and moved in its own function by 7d0bbb6dd730. We actually read the result of this other computation in the very line before the deleted block. I somehow forgot to remove the original code, but it is now dead. Good bye duplicated computation.