Centeralize calculation of which blocks are reserved/used for

Centeralize calculation of which blocks are reserved/used for
the superblock and block group descriptors into two functions:
ext2fs_reserve_super_and_bgd, found in lib/ext2fs/alloc_sb.c, and
ext2fs_super_and_bgd_lock, found in lib/ext2fs/close.c.

Change e2fsck/pass1.c (mark_table_blocks), lib/ext2fs/closefs.c
(ext2fs_flush), lib/ext2fs/initialize.c (ext2fs_initialize),
and misc/dumpe2fs.c (list_desc) to use these functions.

e2fsck/ChangeLog
    pass1.c (mark_table_blocks): Use the new function
    	ext2fs_reserve_super_and_bgd to calculate the blocks to be
    	reserved.

lib/ext2fs/ChangeLog
    closefs.c (ext2fs_super_and_bgd_loc): New function which
    	centralizes the calculation of the superblock and block
    	group descriptors.
    	(ext2fs_flush): Use ext2fs_super_and_bgd_lock to figure
    	out where to write the superblock and block group
    	descriptors.

    alloc_sb.c (ext2fs_reserve_super_and_bgd): New function which
    	reserves space in the block bitmap using
    	ext2fs_super_and_bgd_loc.

    initialize.c (ext2fs_initialize): Use
    	ext2fs_reserve_super_and_bgd to initialize the block bitmap.

misc/ChangeLog
    dumpe2fs.c (list_desc): Use ext2fs_super_and_bgd_loc to
    	determine the locations of the superblock and block group
     	descriptors.