git-send-email.perl: Handle shell metacharacters in $EDITOR properly

git-send-email.perl: Handle shell metacharacters in $EDITOR properly

This fixes the git-send-perl semantics for launching an editor when
$GIT_EDITOR (or friends) contains shell metacharacters to match
launch_editor() in builtin-tag.c. If we use the current approach
(sh -c '$0 $@' "$EDITOR" files ...), we see it fails when $EDITOR has
shell metacharacters:

  $ sh -x -c '$0 $@' "$VISUAL" "foo"
  + "$FAKE_EDITOR" foo
  "$FAKE_EDITOR": 1: "$FAKE_EDITOR": not found

Whereas builtin-tag.c will invoke sh -c "$EDITOR \"$@\"".

Thus, this patch changes git-send-email.perl to use the same method as the
C utilities, and additionally updates t/t9001-send-email.sh to test for
this bug.

Signed-off-by: Bryan Donlan <bdonlan@fushizen.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>