To check a directory's in-use bitmap bit by bit, we use
a pointer to an 8 bit wide unsigned value.
The index used to dereference this pointer is calculated
by shifting the bit index right 3 bits. Then we do a
logical AND with the bit# represented by the lower 3
bits of the bit index.
This is an idiomatic way of iterating through a bit map
with simple bitwise operations.
This commit fixes the bug that we only checked bits
3:0 of each 8 bit chunk, because we only used bits 1:0
of the bit index for the bit# in the current 8 bit value.
This resulted in files not being returned by getdirentries(2).
Change the type of the bit map pointer from `char *' to
`u_int8_t *'.
e7aabf96a4