Minimize differencies between our ext2fs headers and relevant Linux
versions by using EXT2_SB macro to access the superblock fields. Most
of the differencies in access to these fields are now hidden inside
this macro.
- Rename the s_db_per_group field of ext2fs_sb_info to s_gdb_count
to reflect the similar change in Linux headers. New name also seem
to be more appropriate for this field.
- Use proper types for s_first_inode and s_inode_size in-core superblock
fields. Now they reflec types used in the on-disk superblock version.
- Add support for older filesystem revisions that doesn't have proper
s_first_ino and s_inode_size fields in the on-disk superblock. In these
cases predefined values for these fields are used.
- Add simple sanity checks for s_first_inode and s_inode_size correctness.
Reviewed by: bde (previous version)
MFC after: 2 weeks
d6b21c236c