Update sidebar-patch

[yagebu]

First of all thanks for mantaining this tap with a working sidebar patch. After also installing mutt with the sidebar patch on Arch Linux, I noticed it worked slightly differently and had more configuration options. Further investigating, I discovered that the patch at https://github.com/nedos/mutt-sidebar-patch/ hasn't been updated in a while and seems to be based on quite an old version of the patch at http://www.lunar-linux.org/mutt-sidebar. As the one at Lunar Linux seems to be the only one that is well-mantained I think it makes sense to update the sidebar patch. For me it applied and compiled without problems.