Run in an elevated credential mode (root) and let the kernel manage
entitlements. Will result in slightly different behavior but should
not be noticed by most.
Also have special error handling for when branches are invalid and
ENOENT would be returned for getattr and readdir so users understand
what is going on and the runtime interface can still be used to fix
the problem.
* follow-symlinks: allows mergerfs to transparently follow symlinks
* link-exdev: in the event a link returns EXDEV create a symlink instead
* rename-exdev: in the event a rename returns EXDEV move the oldpath and
create a symlink for the newpath