Clone & Restore operations learns to handle checksum on a block count other than 1

These changes update the code producing the checksum and make it aware of
value for blocks_per_checksum other than 1.

BUG: fail to validate the latest checksum

Signed-off-by: Patryck Rouleau <pfrouleau@gmail.com>
Partclone learns to handle various image version

This commit updates load_image_desc() to handle the image by determining its
version. The version written is still 0001.

Signed-off-by: Patryck Rouleau <pfrouleau@gmail.com>
Enable image format version 0002

Add the command line parameters to allow the user to select which features
to use when he clones a file system.

From this point, the image format writen by partclone is 0002.

Signed-off-by: Patryck Rouleau <pfrouleau@gmail.com>