glXCreateNewContext can fail with an X11 Error, if indirect GLX has been disabled on the server. Because of the failure (rather than just returning an error), our es2 pipeline dies without failling back to the sw pipeline.

With the updated X servers, indirect GLX is now disabled by default, and this
will affect Mac, Linux, ...

X Error of failed request: BadValue (integer parameter out of range for operation)
  Major opcode of failed request: 149 (GLX)
  Minor opcode of failed request: 24 (X_GLXCreateNewContext)
  Value in failed request: 0x0
  Serial number of failed request: 25
  Current serial number in output stream: 26

It should be possible to trap the X11 error, detect the failure and fall back properly.