bug#19038: confusing command completion

[Ulrich Windl]

When you type "mkpart p<TAB>" in parted 3.2, "p" is completed to "print" which 
makes no sense (expected was "primary") according to help:
---
(parted) help mkpart                                                      
  mkpart PART-TYPE [FS-TYPE] START END     make a partition

    PART-TYPE is one of: primary, logical, extended
        FS-TYPE is one of: btrfs, nilfs2, ext4, ext3, ext2, fat32, fat16, hfsx,
        hfs+, hfs, jfs, swsusp, linux-swap(v1), linux-swap(v0), ntfs, reiserfs,
        hp-ufs, sun-ufs, xfs, apfs2, apfs1, asfs, amufs5, amufs4, amufs3,
        amufs2, amufs1, amufs0, amufs, affs7, affs6, affs5, affs4, affs3, affs2,
        affs1, affs0, linux-swap, linux-swap(new), linux-swap(old)
        START and END are disk locations, such as 4GB or 10%.  Negative values
        count from the end of the disk.  For example, -1s specifies exactly the
        last sector.
        
        'mkpart' makes a partition without creating a new file system on the
        partition.  FS-TYPE may be specified to set an appropriate partition
        ID.
---

Despite of that the help seems wrong for GPT anyway, because PART-TYPE is used 
as the name (label) of the GPT partition entry.
Please clean up!