A stack trace would be really useful here; obviously it's not crashing for everyone...

Obviously...

The stacktrace is below.  Note that this is an older machine, a HP laptop, with a Radeon Mobility 9100IGP graphics card.  I have had several, as yet unresolved, issues with this card (e.g., https://bugs.freedesktop.org/show_bug.cgi?id=25597), and most recently GL has stopped working properly.

Here's the stactrace

X: ../../../include/privates.h:122: dixGetPrivateAddr: Assertion `key->initialized' failed.

Program received signal SIGABRT, Aborted.
0xb72aec66 in raise () from /lib/libc.so.6
(gdb) thread apply all bt full

Thread 1 (Thread 0xb726b7c0 (LWP 18702)):
#0  0xb72aec66 in raise () from /lib/libc.so.6
No symbol table info available.
#1  0xb72b0571 in abort () from /lib/libc.so.6
No symbol table info available.
#2  0xb72a7e60 in __assert_fail () from /lib/libc.so.6
No symbol table info available.
#3  0xb71e323e in dixGetPrivateAddr (privates=0x826c648, key=0xb71e7e9c)
    at ../../../include/privates.h:122
        __PRETTY_FUNCTION__ = "dixGetPrivateAddr"
#4  0xb71e32a9 in dixGetPrivate (privates=0x826c648, key=0xb71e7e9c)
    at ../../../include/privates.h:137
        __PRETTY_FUNCTION__ = "dixGetPrivate"
#5  0xb71e334a in dixLookupPrivate (privates=0x826c648, key=0xb71e7e9c)
    at ../../../include/privates.h:167
No locals.
#6  0xb71e3379 in DRI2GetScreen (pScreen=0x826c4f0) at dri2.c:112
No locals.
#7  0xb71e4dd4 in DRI2Connect (pScreen=0x826c4f0, driverType=0, fd=0x82aea38, 
    driverName=0xbfacd428, deviceName=0xbfacd424) at dri2.c:959
        ds = 0xb71e4dc3
#8  0xb7237784 in __glXDRIscreenProbe (pScreen=0x826c4f0) at glxdri2.c:704
---Type <return> to continue, or q <return> to quit---
        driverName = 0xbfacd448 "\230Ô¬¿+\206\"·ðÄ&\bó\203\"·"
        deviceName = 0xb72455b8 "hÔ\005"
        screen = 0x82ae9e8
        filename = "ØÎ*\bh\000\000\000h\000\000\000h\000\000\000ô¿<·\220ç*\b`{#\bà\214r·\000\000\000\000øÓ¬¿@7\006\bô¿<·\000\000\000\000 Ñ<·øÓ¬¿Í\027/· Ñ<·\020\000\000\000`{#\bà\214r·\000\000\000\000(Ô¬¿\026\200\006\b\020\000\000\000\001\000\000\000\000\000\000\000?\220\036·\005\000\000\000\000\200\036·ÔÕ\005\000Hâ*\b|Í\004\b"
        buffer_size = 134644858
        pScrn = 0x82620d8
        extensions = 0x824bb94
        driConfigs = 0x82ae248
        i = 134644783
#9  0xb722862b in GlxExtensionInit () at glxext.c:378
        glxScreen = 0x811503b
        extEntry = 0x806cd35
        pScreen = 0x826c4f0
        i = 0
        p = 0xb7247e7c
        glx_provided = 0
#10 0x080d158e in InitExtensions (argc=1, argv=0xbfacd5a4)
    at ../../../mi/miinitext.c:541
        i = 26
---Type <return> to continue, or q <return> to quit---
        ext = 0x82a7e80
        listInitialised = 1
#11 0x0806324e in main (argc=1, argv=0xbfacd5a4, envp=0xbfacd5ac) at main.c:211
        i = 256
        alwaysCheckForInput = {0, 1}

Looks like your driver isn't calling DRI2ScreenInit. Here's a patch which makes DRI2 simply fail in that case:

diff --git a/hw/xfree86/dri2/dri2.c b/hw/xfree86/dri2/dri2.c
index d33b0d1..96a8db4 100644
--- a/hw/xfree86/dri2/dri2.c
+++ b/hw/xfree86/dri2/dri2.c
@@ -956,8 +956,12 @@ Bool
 DRI2Connect(ScreenPtr pScreen, unsigned int driverType, int *fd,
 	    const char **driverName, const char **deviceName)
 {
-    DRI2ScreenPtr ds = DRI2GetScreen(pScreen);
+    DRI2ScreenPtr ds;
+
+    if (!dixPrivateKeyRegistered(dri2ScreenPrivateKey))
+	return FALSE;
 
+    ds = DRI2GetScreen(pScreen);
     if (ds == NULL || driverType >= ds->numDrivers ||
 	    !ds->driverNames[driverType])
 	return FALSE;

I applied the patch,  and now X starts.   I'm using the radeon driver.   

From Xorg.0.log


[ 27850.031] (II) Loading /usr/lib/xorg/modules/drivers/radeon_drv.so
[ 27850.031] (II) Module radeon: vendor="X.Org Foundation"
[ 27850.031]    compiled for 1.8.99, module version = 6.13.99
[ 27850.031]    Module class: X.Org Video Driver

I'll atach the rest of the log file.

Created attachment 36118 [details]
Log file after patch

Shouldn't the patch be committed?

Thanks for testing, this is in commit 505724c5f3e4fc1475fa54f20d08c0c06fb32443