Fixed symlink to isolinux.bin.
Updated symlink to vesamenu.c32.
Updated symlink to hdt.c32.
Added upgrade-basebox command.
Merge branch 'fix-syslinux6'

* fix-syslinux6:
  Updated symlink to hdt.c32.
  Updated symlink to vesamenu.c32.
  Fixed symlink to isolinux.bin.