7.3 Import filesystem callback sequence

1. fc_getparlist() will be called, it should return the struct fs_pars filled in with parameters suitable for subsequent potential fc_mkfs(). All the parameters with up_export flag should be returned by the call of this function.
2. fc_identify() to call try filesystem identification.
3. fc_getparams() is called, it should physically read filesystem specific data for the partition being imported and modify parameters in struct fs_pars. Any parameters specific just for `import' should be added here.

   up_dircount MUST be set to 1. up_dirs->ud_part is not filled in, fixed by Surprise.

4. fc_get_rootdirs() may be optionally called to expand the list of root-located directoties. Currently not implemented/used.
5. fc_get_info() may be optionally called to acquire detailed information about files on filesystem. This info is just for the purposes of the conversion and UI will not be able to display it before the conversion starts. For general filesystem contents information for the user use `import, detected' flagged user parameters returned by fc_getparams() above. After fc_get_rootdirs() gets implemented, this callback can be called for any of the interesting directories returned by it.
6. fc_init() is called right before any `import'-specific functions that follow below.
7. Any import/reading functions.
8. fc_done() when Surprise is done with import of this filesystem.