drag-and-drop failures

[Dave Love]

It's good to see X drag-and-drop support added, but I think it needs
explaining what is expected to work.  Also, presumably the TODO item
on this can now be removed or be amended to say what still needs to be
done.

I can drag text successfully from KDE applications, but not from
Mozilla/Galeon, or OpenWindows.  I'm not surprised OpenWindows won't
work, but NEWS talks about drag and drop `under X' generally.

ASCII characters dragged from Galeon (built for GNOME) or Mozilla get
converted to U+FFFD in Emacs.

Dragging text from CDE dtpad (running on Tru64) to Emacs (on Debian)
crashes Emacs:

Program received signal SIGSEGV, Segmentation fault.
0x70345b04 in _X11TransWrite () from /usr/X11R6/lib/libX11.so.6
(gdb) bt
#0  0x70345b04 in _X11TransWrite () from /usr/X11R6/lib/libX11.so.6
#1  0x70325ca4 in _XFlush () from /usr/X11R6/lib/libX11.so.6
#2  0x70327304 in _XReply () from /usr/X11R6/lib/libX11.so.6
#3  0x70322558 in XSync () from /usr/X11R6/lib/libX11.so.6
#4  0x000959a8 in x_catch_errors_unwind (old_val=5615712)
    at /dl/sr/homes/px/fx/esrc/src/xterm.c:7714
#5  0x00120dc0 in unbind_to (count=400, value=541020088)
    at /dl/sr/homes/px/fx/esrc/src/eval.c:3082
#6  0x00095b70 in x_connection_closed (dpy=0x661198, error_message=0x3ec400 "")
    at /dl/sr/homes/px/fx/esrc/src/xterm.c:7905
#7  0x00095db8 in x_error_quitter (display=0x661198, error=0xefffe6a0)
    at /dl/sr/homes/px/fx/esrc/src/xterm.c:7943
#8  0x00095dfc in x_error_handler (display=0x661198, error=0xefffe6a0)
    at /dl/sr/homes/px/fx/esrc/src/xterm.c:7958
#9  0x70329240 in _XError () from /usr/X11R6/lib/libX11.so.6
#10 0x70327660 in _XReply () from /usr/X11R6/lib/libX11.so.6
#11 0x7030eb70 in XGetAtomName () from /usr/X11R6/lib/libX11.so.6
#12 0x000aa4ac in x_atom_to_symbol (dpy=0x661198, atom=2157853552)
    at /dl/sr/homes/px/fx/esrc/src/xselect.c:290
#13 0x000ac788 in selection_data_to_lisp_data (display=0x661198, 
    data=0x6095d0 "", size=18, type=4, format=536870911)
    at /dl/sr/homes/px/fx/esrc/src/xselect.c:1655
#14 0x000ac5e0 in x_get_window_property_as_lisp_data (display=0x661198, 
    window=37748766, property=305, target_type=541247376, selection_atom=1277)
    at /dl/sr/homes/px/fx/esrc/src/xselect.c:1574
#15 0x000ad0a0 in Fx_get_selection_internal (selection_symbol=544384744, 
    target_type=541247376, time_stamp=541020088)
    at /dl/sr/homes/px/fx/esrc/src/xselect.c:1979
#16 0x0012018c in Ffuncall (nargs=2, args=0xefffea50)
    at /dl/sr/homes/px/fx/esrc/src/eval.c:2730
#17 0x0014e700 in Fbyte_code (bytestr=-268440864, vector=6451168, 
    maxdepth=536870911) at /dl/sr/homes/px/fx/esrc/src/bytecode.c:689
#18 0x00120508 in funcall_lambda (fun=-2141032080, nargs=6, 
    arg_vector=0xefffec84) at /dl/sr/homes/px/fx/esrc/src/eval.c:2910
#19 0x0011fff0 in Ffuncall (nargs=6, args=0xefffec80)
    at /dl/sr/homes/px/fx/esrc/src/eval.c:2780
#20 0x0014e700 in Fbyte_code (bytestr=-268440448, vector=6445664, 
    maxdepth=536870911) at /dl/sr/homes/px/fx/esrc/src/bytecode.c:689
#21 0x00120508 in funcall_lambda (fun=-2141037792, nargs=1, 
    arg_vector=0xefffee44) at /dl/sr/homes/px/fx/esrc/src/eval.c:2910
#22 0x0011fff0 in Ffuncall (nargs=1, args=0xefffee40)
    at /dl/sr/homes/px/fx/esrc/src/eval.c:2780
#23 0x0011baec in Fcall_interactively (function=543315112, 
...
(gdb) f 12
#12 0x000aa4ac in x_atom_to_symbol (dpy=0x661198, atom=2157853552)
    at /dl/sr/homes/px/fx/esrc/src/xselect.c:290
290       str = XGetAtomName (dpy, atom);
(gdb) p atom
$1 = 2157853552
(gdb) pr

Program received signal SIGSEGV, Segmentation fault.
0x001330bc in print_object (obj=-2137113744, printcharfun=541103072, 
    escapeflag=1) at /dl/sr/homes/px/fx/esrc/src/print.c:1392
1392                    strout (buf, -1, -1, printcharfun, 0);
The program being debugged was signaled while in a function called from GDB.
GDB remains in the frame where the signal was received.
To change this behavior use "set unwindonsignal on"
Evaluation of the expression containing the function (debug_print) will be 
abandoned.
(gdb) f 16
#16 0x000aa4ac in x_atom_to_symbol (dpy=0x661198, atom=2157853552)
    at /dl/sr/homes/px/fx/esrc/src/xselect.c:290
290       str = XGetAtomName (dpy, atom);
(gdb) p atom
$2 = 2157853552
(gdb) xsymbol
$3 = (struct Lisp_Symbol *) 0x9e3b70
Cannot access memory at address 0x9e3b74