Detect overflows in loop counters

Detect overflows in loop counters

For loops such as:

for (i=1; i <= fs->super->s_blocks_count; i++) {
        <do_stuff>
}

if i is an int and s_blocks_count is (2^32-1), the condition is never false.
Change these loops to:

for (i=1; i <= fs->super->s_blocks_count && i > 0; i++) {
        <do_stuff>
}

to stop the loop when we overflow i

Signed-off-by: Eric Sandeen <esandeen@redhat.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>