fdisk: (dos) use ask API for new partition dialog

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: (dos) remove remaining read_{int,char}() functions

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: (dos) fix offset dialog unit

Signed-off-by: Karel Zak <kzak@redhat.com>
libfdisk: copy ask callback from parental context

Signed-off-by: Karel Zak <kzak@redhat.com>
fdisk: (bsd) use ask API for add partition dialog

Signed-off-by: Karel Zak <kzak@redhat.com>