A quick & dirty OS4 port of Michal Letowski's xpk.datatype
(http://aminet.net/package/util/dtype/XPKDT-1.0B).

Porting was a bit more "interesting" on this one since for some reason only the
.c files were included in the aminet archive but none of the headers.
Fortunately they weren't too unusual so I could quite easily recreate them from
looking at the sources.

Installation:

1. copy xpk.datatype to SYS:Classes/DataTypes
2. copy XPK and "Power Packer" descriptor files to DEVS:DataTypes

Also you will need OS4 native xpkmaster.library or xpk.l.main glue file in order
to use this datatype.

 PERMSSN    UID  GID    PACKED    SIZE  RATIO METHOD CRC     STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                 3296   10987  30.0% -lh5- 67a3 Dec  4 11:34 xpk_dt-os4/dispatch.c
[generic]                  561    2471  22.7% -lh5- 7636 Dec  4 11:35 xpk_dt-os4/include/classbase.h
[generic]                 2183    6935  31.5% -lh5- 9e92 Dec  4 11:35 xpk_dt-os4/init.c
[generic]                  496     923  53.7% -lh5- bedb Dec  4 11:36 xpk_dt-os4/Makefile
[generic]                   88     100  88.0% -lh5- 60b5 Nov 20  1995 xpk_dt-os4/Power Packer
[generic]                 5435    8306  65.4% -lh5- 9d38 Dec  4 11:36 xpk_dt-os4/Power Packer.info
[generic]                   76      84  90.5% -lh5- 0484 Nov 19  1995 xpk_dt-os4/XPK
[generic]                 3038    6636  45.8% -lh5- 4eaf Dec  4 11:36 xpk_dt-os4/xpk.datatype
[generic]                  121     209  57.9% -lh5- 02bd Dec  4 10:56 xpk_dt-os4/xpk.datatype_rev.h
[generic]                  133     255  52.2% -lh5- 571b Dec  4 10:56 xpk_dt-os4/xpk.datatype_rev.i
[generic]                    2       2 100.0% -lh0- 9795 Dec  4 10:56 xpk_dt-os4/xpk.datatype_rev.rev
[generic]                  136     268  50.7% -lh5- aa6b Dec  4 10:56 xpk_dt-os4/xpk.datatype_rev.s
[generic]                 5435    8306  65.4% -lh5- 6974 Dec  4 11:36 xpk_dt-os4/XPK.info
[generic]                 4142   11016  37.6% -lh5- c594 Nov 21  1995 xpk_dt-os4/XPKDT.guide
[generic]                  402     620  64.8% -lh5- 60bb Dec  4 11:55 xpk_dt-os4/README.OS4
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total        15 files   25544   57118  44.7%            Dec 10 16:36