ext2fs: declare struct_io_manager at end of file

ext2fs: declare struct_io_manager at end of file

Declare struct_io_manager at the end of unix_io.c, undo_io.c, and
test_io.c files so that there isn't a need to forward declare every
member of this structure.  That avoids a lot of redundant code
at the start of every one of these files.

Move the test_flush() function above test_abort() to avoid the need
for a forward declaration.

Fix a few instances of space before tab in these files.

Signed-off-by: Andreas Dilger <adilger@dilger.ca>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>