remote-mediawiki: provide a list form of run_git()

remote-mediawiki: provide a list form of run_git()

Invoking commands as "git $args" doesn't quote $args. Let's support
["git", $args] as well, and create corresponding run_git_quoted() and
run_git_unquoted() aliases for subsequent changes when we move the
code over to the new style of invoking this function. At that point
we'll delete the then-unused run_git() wrapper.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>