* 20050511 njh
- Changed Interval class to match gaol interface.
- inv now handles zero crossings.
- added log, exp, pow(AAF, double)
- pow(AAF, int) now uses russian peasant algorithm
- AAFs can now be Affine, Infinite and/or NAN.  Some work remains to making sure that these are propagated correctly.
- sqrt and log return NAN (domain errors) for negative numbers