Changes in QMBF 5.40:
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- "Plot Options" dialog now allows manual selection of both x and y plot ranges
  (works with Grace v 50122, not tested with other Grace versions)
- new option allowing an arbitrary function of the parameters to be added to chi^2 (see user manual for details)
- new "Type II" matrix models (see user manual for details)
- Bayesian constraints are now disabled by default
- for User-defined Model, numerical differentiation for first derivatives is now enabled by default
- fixed typos in error messages