Xpra: Ticket #207: xpra over ssh X11 forwarding crashes

Instead of using xpra's ssh mode, first connect to the server with ssh -X (or ssh -Y) then run xpra attach.

You may then get this segfault:

#0  __strlen_sse2 () at ../sysdeps/x86_64/strlen.S:32
#1  0x000000346368e52b in PyString_FromString (str=0x0)
    at /usr/src/debug/Python-2.7.3/Objects/stringobject.c:121
#2  0x00007fffea18dc5c in __pyx_pf_8wimpiggy_8lowlevel_8bindings_58get_keycode_mappings
       (__pyx_v_display_source=<optimized out>, __pyx_self=<optimized out>)
    at wimpiggy/lowlevel/bindings.c:11254
#3  __pyx_pw_8wimpiggy_8lowlevel_8bindings_59get_keycode_mappings
      (__pyx_self=<optimized out>, __pyx_v_display_source=<optimized out>)
    at wimpiggy/lowlevel/bindings.c:10997
#4  0x00000034636dd043 in call_function (oparg=<optimized out>, pp_stack=
    0x7fffffffcc58) at /usr/src/debug/Python-2.7.3/Python/ceval.c:4086
#5  PyEval_EvalFrameEx (f=<optimized out>, throwflag=throwflag@entry=0)
    at /usr/src/debug/Python-2.7.3/Python/ceval.c:2740
#6  0x00000034636dcd51 in fast_function (nk=<optimized out>, na=1,
    n=<optimized out>, pp_stack=0x7fffffffce58, func=
    <function at remote 0xe0c230>)
    at /usr/src/debug/Python-2.7.3/Python/ceval.c:4184
#7  call_function (oparg=<optimized out>, pp_stack=0x7fffffffce58)
    at /usr/src/debug/Python-2.7.3/Python/ceval.c:4119
#8  PyEval_EvalFrameEx (f=<optimized out>, throwflag=throwflag@entry=0)
    at /usr/src/debug/Python-2.7.3/Python/ceval.c:2740
#9  0x00000034636dcd51 in fast_function (nk=<optimized out>, na=1,
    n=<optimized out>, pp_stack=0x7fffffffd058, func=