libparted: add nilfs2 module

libparted: add nilfs2 module

* libparted/fs/nilfs2/Makefile.am: New file.
* libparted/fs/nilfs2/nilfs2.c: New file.
(is_valid_nilfs_sb, nilfs2_probe, nilfs2_clobber): New functions.
(ped_file_system_nilfs2_init, ped_file_system_nilfs2_done): Likewise.
(nilfs2_ops, nilfs2_type): Define.
* libparted/fs/Makefile.am (SUBDIRS): Add nilfs2.
* configure.ac (AC_OUTPUT): Add the new Makefile.
* libparted/libparted.c: Declare and use the _init and _done functions.

Add a new fs module to provide following:
- probe nilfs2 filesystem partition
- clobber nilfs2 filesystem partition

The is_valid_nilfs_sb function came from the grub nilfs2 module,
which is written by me and assigned to FSF.