t2060: add a test for switch with --orphan and --discard-changes

t2060: add a test for switch with --orphan and --discard-changes

We have several code paths in the checkout code which are traversed only
in this case, due to switch having different defaults from checkout.
Let's add a test that the combination of options works and produces the
expected behavior.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Reviewed-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>