In reduce_time_seasonal():  If the entering variable has a singleton time axis, get rid of it
exactly the same way that it would be treated if the time axis had been nontrivial and then
reduced to a singleton.  This eliminates some harmless but annoying error messages from VCS
when the time comes to plot.
Properly indent the line which writes a simple plot to a file.  If we had multiple variables in
a plot specification (possible but it isn't happening yet), then this would make a difference.