nilfs2-kmod: use block_page_mkwrite_return

Kernels in RHEL 6.1 have backported block_page_mkwrite_return() and
split the main part of block_page_mkwrite() into a sub routine
__block_page_mkwrite().

This converts nilfs_page_mkwrite() so that it uses
block_page_mkwrite_return() and __block_page_mkwrite().

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
nilfs2-kmod: use new sb freeze mechanism

Kernels in RHEL 6.4 and its clones have backported new file system
freeze mechanism with routines
sb_start_pagefault()/sb_end_pagefault(),
sb_start_intwrite()/sb_end_intwrite(), and
sb_start_write()/sb_end_write().

These are used to provide proper freeze protection.

This applies them to nilfs_page_mkwrite(), nilfs_transcation_begin()
nilfs_transaction_commit(), and nilfs_tranaction_abort().

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
nilfs2-kmod: enable new sb freeze mechanism

Since RHEL 6.4 introduced a new fs_flag FS_HAS_NEW_FREEZE to keep
compatibility of out-of-tree modules, we need to add FS_HAS_NEW_FREEZE
flag to enable new sb freeze mechanism.

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>
nilfs2-kmod: 0.4.5 release

Signed-off-by: Ryusuke Konishi <konishi.ryusuke@lab.ntt.co.jp>