Btrfs: add transaction.h to the Makefile

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

fs/btrfs/Makefile

 CC=gcc
 CFLAGS = -g -Wall -Werror
-headers = radix-tree.h ctree.h disk-io.h kerncompat.h print-tree.h list.h
+headers = radix-tree.h ctree.h disk-io.h kerncompat.h print-tree.h list.h \
+	  transaction.h
 objects = ctree.o disk-io.o radix-tree.o mkfs.o extent-tree.o print-tree.o \
 	  root-tree.o dir-item.o hash.o file-item.o inode-item.o