```
msdosfs_rename(): handle errors from msdosfs_lookup_ino()
Properly working storage and correct filesystem structure indeed only
allow the EJUSTRETURN return code, but since the called function needs
to read directory blocks and (re)parse the content, the assert is not
neccessary hold.
PR: 276408
```
```
msdosfs_rename(): implement several XXXs about downgrading to ro
```
```
msdosfs_integrity_error(): plug possible busy leak
If taskqueue_enqueue() returned error, unbusy().
Handle parallel calls to msdosfs_integrity_error() by unbusying in
msdosfs_remount_ro() up to pending times.
```