xspec 12.5 patches

Another set of recent xspec patches. Two of these are minor mistakes in the 12.5 release, the others cover relatively obscure problems.

12.5.0e	In the FNINIT function (for users linking the XSPEC models library into their own programs), the default model data directory name needs to be updated from "modelIonData" to "modelData" to coincide with v12.5.0 restructuring. Our thanks to John Houck for pointing this out. Report added on Dec 05, 2008.
12.5.0f	Patch to improve the behavior of an exceptional case of Levenberg-Marquardt fitting, where a parameter becomes pegged due to a zero second-derivative matrix diagonal element AND the user chooses to exit before convergence. This prevents an attempt at a covariance calculation on the parameter, which otherwise might lead to a segmentation fault. Our thanks to Stefano Bianchi and Jeremy Sanders for pointing this out. Report added on Dec 05, 2008.
12.5.0g	Fix to the swind1 model function. Now that it is included as part of XSPEC's built-in models library, it should no longer look to the $LMODDIR symbol for finding the model data directory. Our thanks to Delphine Porquet for pointing this out. Report added on Dec 09, 2008.
12.5.0h	When doing a 2-panel plot of plot counts/lcounts chisq and the current fit statistic is cstat, the Y-axis scaling of the chisq panel is wrong. Our thanks to Fill Humphrey for pointing this out. Report added on Dec 09, 2008.