Modified to build under Yosemite using Clang 6.0 and TclTk 8.6, which has deprecated direct use of the Tcl interpreter result field

   This version was modified to build on Yosemite using the latest Clang
   compiler (6.0) and the latest Tcl/Tk (8.6). This needed a very large
   number of changes, mostly to code that made use of the - now deprecated -
   'result' flag of the tcl interpreter. All of these cases needed to be
   changed to use Tcl_SetResult() and Tcl_GetStringResult() in one way or
   another. At the same time, any other code that was generating warnings
   with this recent (and quite fussy) compiler was also modified. This
   version built on my laptop with no warnings at all.

   The files changed were:

   dtclbackgnd.c dtclbshareinit.c dtclcmderror.c dtclcommand.c dtcldits.c
   dtclersrep.c dtclload.c dtclmodule.c dtclreqnot.c dtclrunning.c dtclsds.c
   dtclsdsimg.c dtclshareinit.c dtclstdin.c dtcltk.c dtcltkscreeninfo.c
   gitloggerinit.C

   The file fix.py has been added to the sub-system, just for historical
   interest. It was used to replace as many references to "interp->result"
   in the code as was practical, and the remaining warnings from the compiler
   were fixed by hand. (Note that there were over 350 lines of code that
   contained "interp->result". About 80% (at a rough guess) were handled
   automatically. The rest were harder.