[winswitch] OpenGL Setup Failure

[Bob Babcock]

When I connect from Windows 7 to Linux with Xpra, I get a graphical popup:

OpenGL Setup Failure
constructFunction() got an unexpected keyword argument 'force_extension'

This doesn't seem to break anything.  I suspect it means I need to update 
something on the Linux side, but I don't know what.

Windows side is Xpra 2.3.4 or 2.4-r20214 beta (32-bit)
(Windows version 2.1.1.0 does not trigger this message)

Linux side is Fedora 28.  Xpra routines installed:

    rpm -qa|grep -i xpra
    xpra-common-server-2.3.4-1.r20509.fc28.noarch
    xpra-common-client-2.3.4-1.r20509.fc28.noarch
    python2-xpra-server-2.3.4-1.r20509.fc28.x86_64
    xpra-html5-2.3.4-1.r20509.fc28.noarch
    ffmpeg-xpra-4.0.2-1.fc28.x86_64
    xpra-2.3.4-1.r20509.fc28.x86_64
    x264-xpra-20180401-0.fc28.x86_64
    xpra-common-2.3.4-1.r20509.fc28.noarch
    python2-xpra-client-2.3.4-1.r20509.fc28.x86_64
    xorg-x11-drv-dummy-0.3.8-1.xpra1.fc28.x86_64
    python2-xpra-audio-2.3.4-1.r20509.fc28.x86_64
    python2-xpra-2.3.4-1.r20509.fc28.x86_64

OpenGL routines installed:

    rpm -qa|grep -i opengl
    python3-pyopengl-3.1.1a1-10.fc28.x86_64
    python2-pyopengl-3.1.1a1-10.fc28.x86_64
    libglvnd-opengl-1.1.0-1.fc28.x86_64

A windows bat file sets various environment variables, then starts xpra with the 
line:

    start xpra start --start-child="xterm -xrm XTerm.vt100.allowTitleOps:false
    -title %username%@%host%:%display%" --speaker=off --ssh="plink -ssh -agent
    -P %port%" ssh/%username%@%host%:%port%/%display%

Any suggestions?  Thanks.