Comment 21 for bug 748340

Whoops, meant to include:

2 == (1<<1), which means BTRFS_FEATURE_INCOMPAT_DEFAULT_SUBVOL. git pickaxe points me to commit 6ef5ed last december, which added support for changing the default subvolume. It the incompat flag was set to prevent older kernels from silently mounting the wrong tree; this shouldn't affect the correctness of btrfsck's work however.