Implement multi-bit aligned accessors for sparse bitmap.

Implement multi-bit aligned accessors for sparse bitmap.

Provide set/get routines to allow sparse bitmaps to be treated as an array
of multiple bit values. Only chunk sizes that are powers of 2 are supported.

	* bitmap.c (bitmap_set_aligned_chunk): New.
	(bitmap_get_aligned_chunk): New.
	(test_aligned_chunk): New.
	(bitmap_c_tests): Call test_aligned_chunk.
	* bitmap.h (bitmap_set_aligned_chunk, bitmap_get_aligned_chunk): New.