Btrfs: add a sanity test for btrfs_split_item

While looking at somebodys corruption I became completely convinced that
btrfs_split_item was broken, so I wrote this test to verify that it was working
as it was supposed to.  Thankfully it appears to be working as intended, so just
add this test to make sure nobody breaks it in the future.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Signed-off-by: Chris Mason <chris.mason@fusionio.com>
diff --git a/fs/btrfs/tests/btrfs-tests.h b/fs/btrfs/tests/btrfs-tests.h
index 5808776..04f2cd2 100644
--- a/fs/btrfs/tests/btrfs-tests.h
+++ b/fs/btrfs/tests/btrfs-tests.h
@@ -24,11 +24,16 @@
 #define test_msg(fmt, ...) pr_info("btrfs: selftest: " fmt, ##__VA_ARGS__)
 
 int btrfs_test_free_space_cache(void);
+int btrfs_test_extent_buffer_operations(void);
 #else
 static inline int btrfs_test_free_space_cache(void)
 {
 	return 0;
 }
+static inline int btrfs_test_extent_buffer_operations(void)
+{
+	return 0;
+}
 #endif
 
 #endif