libext2fs: 32-bit bitmap refactorization, part 3

libext2fs: 32-bit bitmap refactorization, part 3

Create new functions ext2fs_{set,get}_{inode,block}_bitmap_range()
which allow programs like e2fsck, dumpe2fs, etc. to get and set chunks
of the bitmap at a time.

Move the representation details of the 32-bit old-style bitmaps into
gen_bitmap.c.

Change calls in dumpe2fs, mke2s, et. al to use the new abstractions.

Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>