fs-mistrust: Improve BadPermission string
To me, "Incorrect permissions on file or directory /path: g=w o=w" implies that the current permissions on /path are 022.
Change the message to "Incorrect permissions: /path is u=rwx,g=rwx,o=rwx; need g-w,o-w", which is closer to chmod syntax and is more useful in non-interactive environments such as CI and support.
Additionally, this corrects the wrong documentation on format_access_bits
.