#50 Multi-thread rendering broken on hyperthreading processors.

[Jason McGuiness]

On a hyperthreading Windows XP box multiple thread
rendering is broken. (Although single thread rendering
works.)

The symptom is that when you press "Start" a dialog
reports that:
1. "There is not enough free memory to create the
optimal number of ... "
2. It correctly recognises the number of render engines
that should be created.
3. That an unknown exception was caught.

It is unknown if this problem affects normal (non-
hyperthreading) multiple-processor machines.

[Jason McGuiness]

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This problem also affects normal multi-processor machines.

Investigation reveals some coding errors in "Render
Engine.cpp" that cause an access violation in all secondary
render engines, which cause them to rapidly crash.
Fortunately to code is sufficiently defensive to recover from
this an continue rendering with only the primary thread.

A fix is in hand and should be released with the next release.