Consider handling accumulator fields more robustly with dynamic landunits

**Bill Sacks < sacks@ucar.edu > - 2017-11-30 16:13:33 -0700**
**Bugzilla Id:** [2542](http://bugz.cgd.ucar.edu/show_bug.cgi?id=2542)
**Bugzilla CC:** erik@ucar.edu, rfisher@ucar.edu,

To fix bug 2526, I plan to make accumulators not accumulate over inactive points. This should fix any egregious issues with accumulator fields with dynamic landunits. However, in some cases (for certain accumulator fields), it could be helpful for a newly-active patch/column to initialize its accumulator field with some reasonable value, based on the value from an existing active patch/column in that gridcell. We could use infrastructure like dynInitColumns for this.

For example, Rosie suggested we may want to do this for one of the accumulators in FATES (which is based on temperature and relative humidity).