Guess is now section head + FFOO_INI_SUFFIX, to allow for customized
config trees.

The (not sure if )written convention is that module's variable names
should be composed as

    FFOO_BAR_BAZ

for variable bearing *baz* in module named *bar*.

The stack now supports passing down parameters to yum, so there's no
need to another case.

Allow passing doen yum arguments like `--enablerepo="*"`

The old name was bad because port is not listening, rather *something* is
listening on the port.  The new name is better because we can extend it
like

    listening_on -u UDP_PORT
    listening_on -s UNIX_SOCKET
    listening_on -a 127.0.0.1 -t 80
    ...

without losing much readability.

This uses even other function __cut_stack to identify two function
names: $caller is the first function on the stack to be be outside
API and is interesting for user so can be used in pretty printer
(typically for debug output).  $internal is name of the wrapper
from this API; this is used to choose the right pretty printer
(debug, warn...).

Make it clear that the assignment must happen, otherwise we might easily
end up wit empty src or mixup between local and caller's local.

For some strange reason, the tee pipe did not work unless stuffed by cat
(all the output pipes remained empty)