Please merge MODIS changes to main development trunk

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In response to feedback from the CESM developers I changed the definition of 
histogram limits in MODIS_simulator/modis_simulator.f90 from HUGE() to 
explicitly defined, very large numbers. This change should not affect answers 
unless the simulator is given optical depths or pressures in the wrong units. 

I'd like these changes to get merged onto the development trunk and eventually 
onto the stable trunk. 

- Robert

Original issue reported on code.google.com by Robert.M.Pincus@gmail.com on 16 Sep 2013 at 5:27