Commits included:
++++
9266ff8 Btrfs: fix ASSERT(list_empty(&cur_trans->dirty_bgs_list)
++++
aa4661f Btrfs: prepare block group cache before writing
----
2e0adf0 fix qgroups
----
777414a Btrfs: fix merge delalloc logic
----
3075d58 Btrfs: account for the correct number of extents for delalloc reservations
----
2fdbf36 Btrfs: just free dummy extent buffers
----
464919a Btrfs: add sanity test for outstanding_extents accounting