Indicate read only mode for directories

[birdie]

Some paths in the system can be read only for a user who's browsing them, either because the permissions forbid to create/modify anything in the current directory, or if a certain directory belongs to a mount point which is mounted read only.

Please, add an indicator saying you cannot modify the current directory, something like "[ro]":

┌<─ /mnt [ro] ─────────────────────────.[^]>┐
│'n     Name           │ Size  │Modify time │
│/..                   │UP--DIR│Nov 17 00:23│

[gotar]

Proper detection of write access requires multiple checks (not only directory mode, but also xattrs and possibly other things). Until mc has decent ACL support this would only misguide people.