* bitmap.c (struct bitmap_descriptor): Remove forward declaration.
(struct bitmap_head_def): Remove desc pointer. Add descriptor_id
field. Reorder fields for pointer alignment.
* bitmap.c: Include vec.h.
(struct bitmap_descriptor): Rename to bitmap_descriptor_d.
(bitmap_descriptor): New typedef, pointer to bitmap_descriptor_d.
Update all struct bitmap_descriptor references.
(next_bitmap_desc_id): New running index for bitmap desciptors.
(bitmap_descriptors): Vec of all bitmap descriptors by descriptor id.
(hash_descriptor, eq_descriptor): Update for struct bitmap_descriptor
change.
(bitmap_descriptor): Rename function to get_bitmap_descriptor.
Stuff newly allocated bitmap descriptor into bitmap_descriptors.
Set the bitmap descriptor id.
(bitmap_register): Lookup bitmap desciptor and store its ID in
the passed bitmap.
(register_overhead): Likewise.
(bitmap_find_bit): Lookup descriptor by id in bitmap_descriptors.
(print_statistics): Update for struct bitmap_descriptor change.