NodeMonitor: Added B_WATCH_CHILDREN flag.

* Added a directory argument for notify_{stat/attribute}_changed().
* This allows to watch only a directory, and get the notifications for
all of its files, not just add/remove entry notifications.

nfs4: support hard links properly

The main purpose of this patch is to prevent VFS from removing a vnode to early
what might have happened if the NFS client knew it had more than one name but
then one of them was deleted. Moreover, all discovered and still valid names
are stored what may be useful in proper file handle recovery when they are
volatile.

This patch fixes both #9558 and #9561.

nfs4: Allow customization of DirectoryCache expiration time

nfs4: Fix #9555: wrong relational operator used

nfs4: Fix CID 991246: use name of the old entry when reporting removal

nfs4: Remove CacheRevalidator

There is no point in periodically revalidating all existing directory caches.
Directory snapshot can be revalidated when readdir is invoked.

nfs4: Fix problems with reading directory entries
* Inode::ReadDir missed an entry when given buffer was too small
* Each OpenDirCookie now has its own copy of directory snapshot what
would prevent Inode::ReadDir from accessing freed memory when removing
files and reading directory entries simultaneously
* Several minor issues fixed

nfs4: Add numerous assertion checks

nfs4, dns_resolver: fix numerous style violations

nfs4: Fix some cache revalidator problems

nfs4: Update FileInfo at rename

nfs4: Fix file handle recovery

nfs4: Make the client more configurable

nfs4: Add node to inode to file handle map before notifying

nfs4: Get correct change value for attribute directories

nfs4: Fix directory cache revalidation when cache invalid

nfs4: Inode::GetDirSnapshot should not require OpenDirCookie

nfs4: Add attribute directory related hooks

nfs4: Implement node monitoring

nfs4: Local creation of node should not invalidate the cache

nfs4: Add full directory cache implementation

nfs4: Add directory and name basic implementation

nfs4: support hard links properly

The main purpose of this patch is to prevent VFS from removing a vnode to early
what might have happened if the NFS client knew it had more than one name but
then one of them was deleted. Moreover, all discovered and still valid names
are stored what may be useful in proper file handle recovery when they are
volatile.

This patch fixes both #9558 and #9561.

nfs4: Allow customization of DirectoryCache expiration time

nfs4: Fix #9555: wrong relational operator used

nfs4: Fix CID 991246: use name of the old entry when reporting removal

nfs4: Remove CacheRevalidator

There is no point in periodically revalidating all existing directory caches.
Directory snapshot can be revalidated when readdir is invoked.

nfs4: Fix problems with reading directory entries
* Inode::ReadDir missed an entry when given buffer was too small
* Each OpenDirCookie now has its own copy of directory snapshot what
would prevent Inode::ReadDir from accessing freed memory when removing
files and reading directory entries simultaneously
* Several minor issues fixed

nfs4: Add numerous assertion checks

nfs4, dns_resolver: fix numerous style violations

nfs4: Fix some cache revalidator problems

nfs4: Update FileInfo at rename

nfs4: Fix file handle recovery

nfs4: Make the client more configurable

nfs4: Add node to inode to file handle map before notifying

nfs4: Get correct change value for attribute directories

nfs4: Fix directory cache revalidation when cache invalid

nfs4: Inode::GetDirSnapshot should not require OpenDirCookie

nfs4: Add attribute directory related hooks

nfs4: Implement node monitoring

nfs4: Local creation of node should not invalidate the cache

nfs4: Add full directory cache implementation

nfs4: Add directory and name basic implementation