Allows marking in text.datatype and subclasses.

Now you can select areas of the text, and write, print, or copy to clipboard these
selected area.

This update fixes one (maybe serious) bug, and adds a patch when drag-moving
the text (e.g. if the text is colored, the scolling does not work properly; this
patch fixes this).

 PERMSSN    UID  GID    PACKED    SIZE  RATIO     CRC       STAMP          NAME
---------- ----------- ------- ------- ------ ---------- ------------ -------------
[generic]                 2557    4068  62.9% -lh5- ae63 Mar 12  1997 markabletextdtclass/markabletextdtclass
[generic]                 7629   26044  29.3% -lh5- 5e46 Mar 12  1997 markabletextdtclass/markabletextdtclass.c
[generic]                  251     486  51.6% -lh5- 4287 Aug 25  1996 markabletextdtclass/markabletextdtclass.c.info
[generic]                 2387    5200  45.9% -lh5- 34f2 Mar 12  1997 markabletextdtclass/markabletextdtclass.doc
[generic]                  392     835  46.9% -lh5- b0e8 Aug 25  1996 markabletextdtclass/markabletextdtclass.info
[generic]                 4334    7536  57.5% -lh5- 5f22 Mar 12  1997 markabletextdtclass/markabletextdtclass.ld
[generic]                  123     216  56.9% -lh5- 1ff7 Mar 12  1997 markabletextdtclass/markabletextdtclass_rev.h
[generic]                  135     258  52.3% -lh5- f574 Mar 12  1997 markabletextdtclass/markabletextdtclass_rev.i
[generic]                    2       2 100.0% -lh0- c796 Mar 12  1997 markabletextdtclass/markabletextdtclass_rev.rev
[generic]                  955    3724  25.6% -lh5- da69 Mar 12  1997 markabletextdtclass/SMakefile
[generic]                  253     486  52.1% -lh5- 8558 May 18  1996 markabletextdtclass/SMakefile.info
---------- ----------- ------- ------- ------ ---------- ------------ -------------
 Total        11 files   19018   48855  38.9%            Mar 15  1997