fixed a printing bug in mh.c

When printing a fit check after MCMC simulations, the model prediction 
and data values were printed wrong
and mismatched if the Print and Data statements did follow the same 
order in the simulation input file. That did not affect
the results of MCMC simulations at all, but would eventually mess up the 
fit check.
That is now fixed (the latest version of the file is available on

http://cvs.savannah.gnu.org/viewvc/mcsim/sim/?root=mcsim)

F. Bois