flow: change how "for (i = 0; ; i++) { ..." is handled

flow: change how "for (i = 0; ; i++) { ..." is handled

In the old code the i++ was ignored.  But now we take it even though we
ignore all the other state changes.  Now the following code:

	j = 0;
        for (i = 0; ; i++) {
                if (x == 3)
                        break;
                j++;
        }

        __smatch_implied(i);
        __smatch_implied(j);

Gives:
test.c:20 func() implied: i = '0-max'
test.c:21 func() implied: j = '0'

Which is still not right, but it's improved.  I really need to look at how
--two-passes should work again and fix how loops are handled.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>