mke2fs: add make_hugefile feature

mke2fs: add make_hugefile feature

This feature is enabled via settings in /etc/mke2fs.conf.  For
example:

	hugefile = {
		features = extent,huge_file,flex_bg,uninit_bg,dir_nlink,extra_isize,^resize_inode,sparse_super2
		inode_size = 128
		num_backup_sb = 0
		packed_meta_blocks = 1
		make_hugefiles = 1
		inode_ratio = 4194304
		hugefiles_dir = /database
		hugefiles_uid = 120
		hugefiles_gid = 50
		hugefiles_name = storage
		hugefiles_digits = 4
		hugefiles_size = 1G
		num_hugefiles = 0
	}

Then "mke2fs -T hugefile /dev/sdXX" will create as many 1G files
needed to fill the file system.

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