v.support and DLG format

[Bill Brown]

Putting the empty file in dig_plus should work, but here's a 
more permanent fix:

HTTP REF: http://www.cecer.army.mil/grass/faqtxt1.html#gf_415sup

----------------------------
Fix for 4.1.5 v.support. 

If your GRASS distribution came from the complete 4.1.5 
source code from moon, you could have this bug. 
This bug is NOT present in the CERL binary distributions 
of 4.1.5 NOR in the 4.1.4 -> 4.1.5 updates. 

   1.Replace the file src/mapdev/Vlib/level_two.c with this one. 
   2.rm src/libes/$(LIBARCH)/libvect.a 
   3.cd src/mapdev/Vlib; gmake4.1 
   4.rm $GISBASE/etc/v.build 
   5.cd src/mapdev/v.build; gmake4.1 
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- Bill