Fix various signed/unsigned gcc warnings

Some of these could affect filesystems between 2^31 and 2^32-1 blocks.

Thanks to Valerie Aurora Henson for pointing out the problems in
lib/ext2fs/alloc_tables.c, which led me to do a "make gcc-wall" scan
over the source tree.

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