libext2fs: openfs() musn't allow bigalloc without EXT2_FLAGS_64BITS

libext2fs: openfs() musn't allow bigalloc without EXT2_FLAGS_64BITS

Currently, only the new 64-bit bitmap implementation supports the
block<->cluster conversions that bigalloc requires.  Therefore, if we
have a bigalloc filesystem, require EXT2_FLAGS_64BITS be passed in to
ext2fs_open().  This does not mean that bigalloc file systems have to
be 64-bits; just that the userspace utilities have to be able to use
the new 64-bit capable library functions.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: "Theodore Ts'o" <tytso@mit.edu>
Reviewed-by: Lukas Czerner <lczerner@redhat.com>