Btrfs: tweak the inode-map and free extent search starts on cold mount

Signed-off-by: Chris Mason <chris.mason@oracle.com>

diff --cc fs/btrfs/TODO
Simple merge

diff --cc fs/btrfs/ctree.h
Simple merge

diff --cc fs/btrfs/disk-io.c
Simple merge

diff --cc fs/btrfs/extent-tree.c
Simple merge

diff --cc fs/btrfs/inode-map.c
Simple merge