BitMap::reallocate might not clear some bits

If BitMap::reallocate is called with clear == true, it is possible that some bits in the new array that ought to be cleared won't be.

If new_size_in_bits > old_size_in_bits and old_size_in_bits is not word aligned, the word-copy from old to new will copy the entire last word of old, including possibly set bits beyond old_size_in_bits. The requested clearing of new will start with the word following that last copied word. This leaves the bits of new in the range

[old_size_in_bits, word_align_up(MIN2(new_size_in_bits, old_size_in_bits)))

in an unspecified state.