libext2fs: fix binary and source compatibility with the dump program

libext2fs: fix binary and source compatibility with the dump program

The dump program relies on fs->frag_size and the
EXT2_FRAGS_PER_BLOCK() macro.  Kind of silly for it to do so, but it's
part of the kludgy way the dump program (which was originally written
for the BSD FFS was ported over to support ext2/3.)  Given how it
makes assumptions about the ext2/3/4 file system being similar to the
BSD FFS, it's a bit of a miracle it works for ext4 --- or at least
appears to work...

Addresses-Debian-Bug: #636418

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>