Allow imce on non-writable directories.

Issue Summary

Hi,
I want to allow file selection for an imceimage field, where the files are not uploaded via the website, but via something else (sftp, whatever).
This means, the directories don't need to be writable by the web server.

Still, the function imce_check_directory() will only allow directories that are writable. Otherwise, it will refuse to even display the dir contents.
Is this intended? Can this be configured somewhere?

(if not, we could turn this into a feature request)

Thanks!
(btw, imceimage is no longer deprecated, I'm going to bring it back to life :) )