send-email: allow aliases in patch header and command script outputs

send-email: allow aliases in patch header and command script outputs

Interpret aliases in:

  -  Header fields of patches generated by git format-patch
     (using --to, --cc, --add-header for example) or
     manually modified. Example of fields in header:

      To: alias1
      Cc: alias2
      Cc: alias3
  -  Outputs of command scripts specified by --cc-cmd and
     --to-cmd. Example of script:

      #!/bin/sh
      echo alias1
      echo alias2

Signed-off-by: Remi Lespinet <remi.lespinet@ensimag.grenoble-inp.fr>
Signed-off-by: Matthieu Moy <Matthieu.Moy@imag.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>