Btrfs Progs v3.16

Signed-off-by: Chris Mason <clm@fb.com>
btrfs-progs: Do not free dirty extent buffer

free_some_buffer() should not free dirty extent buffers. They are left
to be committed.

Signed-off-by: Naohiro Aota <naota@elisp.net>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: remove unused flags for btrfs_path

The three flags of @btrfs_path:
	btrfs_path {
		unsigned int keep_locks:1;
		unsigned int skip_locking:1;
		unsigned int leave_spinning:1;
	}
have little meaning, because the userspace @btrfs_search_slot()
is free of locking and no other routines will decide their behavior
on these. So just remove them.

Signed-off-by: Gui Hecheng <guihc.fnst@cn.fujitsu.com>
Signed-off-by: David Sterba <dsterba@suse.cz>
btrfs-progs: read global reserve size from space infos

Kernels >= 3.15 export the global block reserve as a space info presented
by 'btrfs fi df' but would display 'unknown' instead of some meaningful
string.

Signed-off-by: David Sterba <dsterba@suse.cz>