This is a new incarnation of compatible_eul(), a function called:
void Mat3ToCompatibleEul(float mat[][3], float *eul, float *oldrot)
It uses the two euler extraction methods as added by Brecht a while ago,
and checks for compatibility each, and then picks the best of the two
based on minimal difference with 'oldrot'.
Gives for rotation key inserting a much higher hitrate for OK eulers.
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