This patch converts reiserfs to use the new export_operations
interface for exporting a filesystem instead of the old
fh_to_dentry and dentry_to_fh.
Essentially it:

  - renamed reiserfs_dentry_to_fh to reiserfs_encode_fh
  - split reiserfs_fh_to_dentry into reiserfs_get_dentry
    and reiserfs_decode_fh
  - calls d_splice_alias from reiserfs_lookup so that building
    a dcache path from the bottom works well
  - addes reiserfs_get_parent to do a lookup of ".." without going
    through the VFS interfaces.
  - sets sb->s_export_op to be an appropriately initialised
    struct export_operations

This has been tested and works.