Btrfs: Fixes for 2.6.28-rc API changes

* open/close_bdev_excl -> open/close_bdev_exclusive
* blkdev_issue_discard takes a GFP mask now
* Fix blkdev_issue_discard usage now that it is enabled

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

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

diff --cc fs/btrfs/compression.c
Simple merge

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

diff --cc fs/btrfs/extent_io.c
Simple merge

diff --cc fs/btrfs/version.sh
Simple merge

diff --cc fs/btrfs/volumes.c
Simple merge

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