contrib/subtree: stop using `-o` to test for number of args
Functions in git-subtree.sh all assert that they are being passed the
correct number of arguments. In cases where we accept a variable number
of arguments we assert this via a single call to `test` with `-o`, which
is discouraged by our coding guidelines.
Convert these cases to stop doing so. This requires us to decompose
assertions of the style `assert test $# = 2 -o $# = 3` into two calls
because we have no easy way to logically chain statements passed to the
assert function.
Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>