libext2fs: 32-bit bitmap refactorization, part 1

libext2fs: 32-bit bitmap refactorization, part 1

Move the 32-bit specific bitmap code into gen_bitmap.c, and the
high-level interfaces into bitmaps.c.  Eventually we'll move the
new-style bitmap code into gen_bitmap64.c, but first we need to
isolate the code with knowledge of the bitmap internals in one place
first.

In this patch we move allocation, free, copy, clear, set_padding, and
fudge_end function into gen_bitmap.c, and make sure that the bitmaps.c
and bitops.c no longer have any knowledge of the bitmap internals.

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