cleaned up chile2010/maketopo.py
changed fgmax_read to take tstart_max and tend_max on two separate lines, other cleanup
changed fgmax_values to set value to large negative number in regions where h is 0
changed fgmax code to take only one min_level_check parameter rather than separate ones for arrivals and max since these were not both used properly.  Also renamed dt_for_max as dt_check since it is used also for arrivals.
Merge pull request #48 from rjleveque/fgmax_updates

Fgmax updates