Add the ability to use a command line --to-cmd=cmd
to create the list of "To:" addresses.
Used a shared routine for --cc-cmd and --to-cmd.
Did not use IPC::Open2, leaving that for Ævar if
ever he decides to fix the other bugs he might find.
Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>