Changed `out' parameter of `assert_bash_exec()' to accept also -1 and 0:
@param mixed $out (optional) Reference to variable to hold output.
If variable equals -1 (default) the bash command is
expected to return no output. If variable equals 0,
any output from the bash command is disregarded.
This fixes the situation of commit cfcf9fa where contrib/ri was causing
invisible errors when running the test suite.
9501c0fa90