Fixing "Fixing default sectors per cluster for FAT32" for UEFI.

FAT32 "EFI System Partition" is basically required for UEFI boot;
commit ge048a8d broke that for me with both virtualbox-4.2 and
real hardware (ASUS C60M1-I to be exact) given ~250Mb filesystem.

This commit amends that one by reverting its effects for these
small sizes by restoring 512b cluster size for <= 260Mb FAT32.

Signed-off-by: Daniel Baumann <mail@daniel-baumann.ch>
Reformating mkfs.fat manpage.

Signed-off-by: Daniel Baumann <mail@daniel-baumann.ch>
Releasing version 3.0.23.

Signed-off-by: Daniel Baumann <mail@daniel-baumann.ch>