send-email: multiedit is a boolean config option

The sendemail.multiedit variable is meant to be a boolean.
However, it is not marked as such in the code, which means
we store its value literally. Thus in the do_edit function,
perl ends up coercing it to a boolean value according to
perl rules, not git rules. This works for "0", but "false",
"no", or "off" will erroneously be interpreted as true.
Signed-off-by: NJeff King <peff@peff.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

git-send-email.perl

@@ -210,6 +210,7 @@ sub do_edit {
     "signedoffbycc" => [\$signed_off_by_cc, undef],
     "signedoffcc" => [\$signed_off_by_cc, undef],      # Deprecated
     "validate" => [\$validate, 1],
+    "multiedit" => [\$multiedit, undef]
 );
 
 my %config_settings = (
@@ -227,7 +228,6 @@ sub do_edit {
     "bcc" => \@bcclist,
     "suppresscc" => \@suppress_cc,
     "envelopesender" => \$envelope_sender,
-    "multiedit" => \$multiedit,
     "confirm"   => \$confirm,
     "from" => \$sender,
     "assume8bitencoding" => \$auto_8bit_encoding,