bash: Add long option completion for 'git send-email'

bash: Add long option completion for 'git send-email'

Add the following long options to be completed with 'git send-email':

    --bcc --cc --cc-cmd --chain-reply-to --compose --dry-run
    --envelope-sender --from --identity --in-reply-to
    --no-chain-reply-to --no-signed-off-by-cc --no-suppress-from
    --no-thread --quiet --signed-off-by-cc --smtp-pass --smtp-server
    --smtp-server-port --smtp-ssl --smtp-user --subject --suppress-cc
    --suppress-from --thread --to

Short ones like --to and --cc are not usable for actual completion
because of the shortness itself and because there are longer ones which
start with same letters (--thread, --compose). It's still useful to have
these shorter options _listed_ when user presses TAB key after typing
two dashes. It gives user an idea what options are available (and --to
and --cc are probably the most commonly used).

Signed-off-by: Teemu Likonen <tlikonen@iki.fi>
Signed-off-by: Junio C Hamano <gitster@pobox.com>