parse-options: teach "git cmd -h" to show alias as alias

parse-options: teach "git cmd -h" to show alias as alias

There is a long-standing NEEDSWORK comment that complains about
inconsistency between how an aliased option ("git clone --recurse"
which is the only one that currently exists) gives a help text in
a usage-error message vs "git cmd -h").  Get rid of it and then
make sure we say an option is an alias for another, instead of
repeating the same short help text for both, which leads to "they
seem to do the same---is there any subtle difference?" puzzlement
to end-users.

Signed-off-by: Junio C Hamano <gitster@pobox.com>