6902459566 was an attempt to not print
$status twice in the prompt. As a result we print $pipestatus but
not $status, which /usually/ is the same as $pipestatus[-1] --- unless
the builtin "not" is used, which inverts the $status of a job (it does
not alter $pipestatus).
As a result, the default prompt prints unexpected status codes:
~ > not false
~ [1]> not true
~ > not true | true
~ > not false | false
~ [1|1]>
This commit reintroduces printing of $status after $pipestatus, but only
if it is different from $pipestatus[-1].
Additionally, we only print anything at all if the $status is nonzero,
to avoid confusing output on `not false | false`
~ > not false
~ > not true
~ [0] 1> not true | true
~ [0|0] 1> not false | false
~ >
I think this is closer to users' expectations for those cases; they should
not have to think about this implementation detail of the not-statement.
5d135d5556