Update mew-regex-ignore-scan-body-list for a line beginning with "["

Please merge this patch not to display a line beginning with "[" in Summary.

e.g. <http://lists.gnu.org/archive/html/emacs-devel/2014-01/msg01657.html>
displays "[[[ To any NSA and FBI ..." in Summary.  With this patch,
"I don't know why ..." is displayed.