Fixed fsd_detach.
Deleted fsd_callback_free (it's unnecessary, becuase when vfs_t is
being destroyed, hook remove callbacks are being fired).
Fixed unprotected fsd_enabled in fsd_ioctl() issue.
Eliminated recursive calls from hooks execution in fsh.
Adjusted fsd code to this changes.
Comments in fsh and fsd aren't yet adjusted to this changes.
fsd naming changes.
Small fsd bugfix with hook instance data.
fsh made invulnerable to {mount,free}, {mount,free} callback
installation in {mount,free} callback. (previously caused a deadlock)