Log Message:
Update darts to 0.31.

pkgsrc change:

  o Add DESTDIR supoprt.
  o fix buildlink3.mk, stopping pkglint's warning.

darts change from 0.2 to 0.31.

  o Change license from LGPL to BSD/LGPL dual license.
  o Fix a bug which cause illegal access when create doule array.
  o Change some methods' name, such as setArray to set_array.
  o Stop providing rpm packages.