Use longer alias names in subdirectory tests

Use longer alias names in subdirectory tests

When testing aliases in t/t1020-subdirectory.sh use longer names so that
they're less likely to conflict with a git-* command somewhere in the
$PATH.

I have a git-ss command in my path which prevents the 'ss' alias from
being used.  This command will always fail for git.git, causing the test
to fail.  Even if the command succeeded, that would be a false success
for the test since the alias wasn't actually used.  A longer, more
descriptive name will make it much less likely that somebody has a
command in their $PATH which will shadow the alias created for the test.

While here, use a longer name for the 'test' alias as well since that is
also short and meaningful enough to make it not unlikely that somebody
would have a command in their $PATH which will shadow that as well.

Signed-off-by: Aaron Schrab <aaron@schrab.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>