Add a hook_upload_path()

It would be great to have the possibility allows other mudules to change the directory of uploaded files.

For example it would allows to put the files into folders depending on the date (something like:)
_ YEAR (for example: 2008)
- \_ MONTH (for example: 03)
--- \_ DAY (for example: 08)
------ \_ HOUR (i think you did understand the concept)

or depending on the user and file type
_ UID
- \_ FILETYPE