e2fsprogs: Undo I/O manager

["Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>]

This is a very early prototype of what i working on. I have done only minimal
testing of this. To use one need to use the below steps.


       io_manager io_mng = stack_io_manager_init();
       stack_push_io_manager(io_mng, unix_io_manager);
       stack_push_io_manager(io_mng, undo_io_manager);
       flags = EXT2_FLAG_SOFTSUPP_FEATURES | EXT2_FLAG_RW;
       retval = ext2fs_open2(dev_name,"tdbfilename=/tmp/test.tdb&",
                                       flags, superblock, block_size,
                                       io_mng, &current_fs);

I am sending this across to find out if this is the approach that we want to follow.

-aneesh