Do not over-quote the -f envelopesender value.

Without this, the value passed to sendmail would have an extra set of
single quotes.  At least exim's sendmail emulation would object to that:

    exim: bad -f address "'list-addr@example.org'": malformed address: ' \
      may not follow 'list-addr@example.org
    error: hooks/post-receive exited with error code 1

Signed-off-by: Jim Meyering <jim@meyering.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

contrib/hooks/post-receive-email

@@ -571,6 +571,15 @@ generate_delete_general_email()
 	echo $LOGEND
 }
 
+send_mail()
+{
+	if [ -n "$envelopesender" ]; then
+		/usr/sbin/sendmail -t -f "$envelopesender"
+	else
+		/usr/sbin/sendmail -t
+	fi
+}
+
 # ---------------------------- main()
 
 # --- Constants
@@ -607,13 +616,8 @@ if [ -n "$1" -a -n "$2" -a -n "$3" ]; then
 	# resend an email; they could redirect the output to sendmail themselves
 	PAGER= generate_email $2 $3 $1
 else
-	if [ -n "$envelopesender" ]; then
-		envelopesender="-f '$envelopesender'"
-	fi
-
 	while read oldrev newrev refname
 	do
-		generate_email $oldrev $newrev $refname |
-		/usr/sbin/sendmail -t $envelopesender
+		generate_email $oldrev $newrev $refname | send_mail
 	done
 fi