When running X11 applications over a tunnelled SSH connection, most extensions
are not present.  This used to work with Slackware 9 (XFree86, not Xorg).  After
upgrading to Slackware 10.1 (Xorg), extensions are broken.

Here's xpdyinfo for a local and then a tunnelled connection:

------ Logged in via xdm
ross@turalyon:~$ xdpyinfo
name of display:    :0.0
version number:    11.0
vendor string:    The X.Org Foundation
vendor release number:    60801000
X.Org version: 6.8.1
maximum request size:  16777212 bytes
motion buffer size:  256
bitmap unit, bit order, padding:    32, LSBFirst, 32
image byte order:    LSBFirst
number of supported pixmap formats:    7
supported pixmap formats:
    depth 1, bits_per_pixel 1, scanline_pad 32
    depth 4, bits_per_pixel 8, scanline_pad 32
    depth 8, bits_per_pixel 8, scanline_pad 32
    depth 15, bits_per_pixel 16, scanline_pad 32
    depth 16, bits_per_pixel 16, scanline_pad 32
    depth 24, bits_per_pixel 32, scanline_pad 32
    depth 32, bits_per_pixel 32, scanline_pad 32
keycode range:    minimum 8, maximum 255
focus:  window 0x140003c, revert to PointerRoot
number of extensions:    32
    BIG-REQUESTS
    DAMAGE
    DEC-XTRAP
    DOUBLE-BUFFER
    DPMS
    Extended-Visual-Information
    GLX
    LBX
    MIT-SCREEN-SAVER
    MIT-SHM
    MIT-SUNDRY-NONSTANDARD
    RANDR
    RECORD
    RENDER
    SECURITY
    SGI-GLX
    SHAPE
    SYNC
    TOG-CUP
    X-Resource
    XC-APPGROUP
    XC-MISC
    XFIXES
    XFree86-Bigfont
    XFree86-DGA
    XFree86-DRI
    XFree86-Misc
    XFree86-VidModeExtension
    XInputExtension
    XKEYBOARD
    XTEST
    XVideo
------------------

-------- Connected via "ssh -X ross@localhost"
ross@turalyon:~$ xdpyinfo
name of display:    localhost:12.0
version number:    11.0
vendor string:    The X.Org Foundation
vendor release number:    60801000
X.Org version: 6.8.1
maximum request size:  16777212 bytes
motion buffer size:  256
bitmap unit, bit order, padding:    32, LSBFirst, 32
image byte order:    LSBFirst
number of supported pixmap formats:    7
supported pixmap formats:
    depth 1, bits_per_pixel 1, scanline_pad 32
    depth 4, bits_per_pixel 8, scanline_pad 32
    depth 8, bits_per_pixel 8, scanline_pad 32
    depth 15, bits_per_pixel 16, scanline_pad 32
    depth 16, bits_per_pixel 16, scanline_pad 32
    depth 24, bits_per_pixel 32, scanline_pad 32
    depth 32, bits_per_pixel 32, scanline_pad 32
keycode range:    minimum 8, maximum 255
focus:  window 0x140003c, revert to PointerRoot
number of extensions:    3
    BIG-REQUESTS
    LBX
    XC-MISC