Apply the ignore-case volume option when preparing the SYS:LOGIN
directory path during connection setup.
With SYS configured as `itO`, the installed tree may use lowercase
Unix directories such as `login/`, but the connection code still tried
to stat the hard-coded uppercase `LOGIN/` path. This caused new client
connections to abort with:
Stat error LOGIN Directory, Abort !!: No such file or directory
UnixPath=`.../SYS/LOGIN/`
Treat `VOL_OPTION_IGNCASE` like `VOL_OPTION_DOWNSHIFT` for this path so
the login directory is resolved as `login/` on ignore-case volumes.