Add a test for the interaction between explicitly provided refspecs
and fetch.prune.
There's no point in adding this boilerplate to every combination of
unset/false/true, it's instructive and sufficient to show that no
matter if the variable is unset, false or true the refspec on the
command-line overrides any configuration variable.
Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com> Signed-off-by: Junio C Hamano <gitster@pobox.com>