[Fractdev] Xfractint and .tga files

Tim, We need to take any Unix specific code in diskvidu.c and move it into diskvid.c (and change the Makefile to use it). There are changes in diskvid.c that I made to fix the problems we were having with the .tga file format. These changes obviously didn't get transferred over to diskvidu.c. Another reason I'd like to do this is that we normally reserve the use of extra Unix files to code that was in an assembly language file. Don't know why it was done to a C file, but we should fix it. Jonathan